The heroes in Dota 2 are defined by the roles that they are suited to play as a combination of their attributes, skills, and items, and the ways that these shape the game. Although the abilities of heroes may suit a variety of purposes and can be used in a variety of ways in different situations, roles nonetheless exist to define the playstyle a hero is expected to conform to, as well as the actions they are meant to perform within a game.
The attributes of heroes (their essential statistics and their basic combat ability) and the varying nature and effects of their abilities all serve to provide much distinction between heroes, giving them each tactical advantages and disadvantages at various locations, situations, and times within the game that have to be understood well for success. As strategic combat between two teams of five heroes with distinctly different abilities and strengths is the central conflict of Dota 2, players need to be well informed of their role within each team as well as the roles of the players on the opposing team so that they know, for example, the highest priority enemy target in a teamfight.
Even more importantly, players should keep in mind how their skill build and item build affects their heroes and fares against the skill and item builds of enemy heroes in the context of every single game so that they make sound decisions on the abilities and items that they choose to get.
 Main Roles
Roles are dictated by many factors, including: the physical stats of the hero, what they bring to the table with their abilities as well as the nature of their abilities, where they should be laned (or jungled), and the amount of gold and items they need to perform well. Although the roles that a hero belong to are fairly set in stone prior to a game, they can and do change within the game itself as a result of multiple factors, so it is up to the player to adapt to the game as it progresses.
 Lane Support
"Helpful in the early-game laning in protecting your team's carry."
Lane Supports or Babysitters are support Heroes who help their team's Carry control the lane in the early stages of the game. They are able to either repel enemies from your team's carry and thus keep them safe, or to allow the carry to continuously stay in the lane using abilities that replenish either health or mana. Common traits of Lane Supports are long-ranged right-click attacks and abilities that are highly useful from level 1 and up. They should always lane with the team's Hard Carry, as aside from supporting them, their lack of dependence on gold and levels means said Carry can take all the farm for themselves without running the risk of soloing a lane. They and the carry almost invariably lane together in the "safe lane" (bot for Radiant and top for Dire), as this is the most difficult lane to gank.
"Will become more useful later in the game if they gain a significant gold advantage."
Carries are the heroes that can obtain the greatest power and utility as the game progresses. (It is so derived from the act being "carried" by a team into the late game; that is, to eventually bear the responsibility for ultimate victory.) They tend to be those who become extremely powerful later in the game as compared to other heroes once they amass enough levels and items. They are the ones expected to have the highest number of kills at the conclusion of the game and tend to be those that directly tackle the structures and the Ancient upon the team becoming powerful enough. Carries typically lack early game power, but they scale well by late game; thus, the items they carry are an essential part of their build. Most carries rely on right-clicking, using sheer attack power to overwhelm their enemies. Carries tend to have high base movement speed.
Although they are the powerhouses of the late game, their weaknesses in the early game are more prominent, and can weigh their team down as they focus more on amassing gold and experience rather than assisting in early game skirmishes. Strength carries (such as Alchemist and Lifestealer) typically rely on sustained damage and their own durability to carry, as well as some decent disables. Agility carries (such as Luna and Phantom Assassin) tend to inflict substantial damage in rapid successions, but often lack disables and durability. Intelligence carries (such as Storm Spirit and Outworld Devourer) usually rely on their abilities and active use of items, but their physical damage is often respectable too.
Some carries with long-cooldown, teamfight-oriented ultimates, such as Naga Siren, Luna and Outworld Devourer require constant team support all throughout the game, whereas other carries such as Phantom Assassin or Lifestealer are suited to tackling many enemies in succession and rely much less on their team (but suffer from a lack of AoE abilities). Essentially, while some carries are suited to solo encounters and ganks, others are most at home in a large clash.
Carries typically are relegated to a side lane early on with one or more Support/Babysit heroes to babysit them until they collect the necessary items to farm independently, while a select few carry heroes, most notably Shadow Fiend and Tinker, can easily undertake a solo midlane role throughout the majority of the game. There are some cases where carries ended up in solo safe lane(Radiant Bottom, Dire Top) if the team opted to run an aggressive tri-lane at the suicide lane(Radiant Top, Dire Bottom).
"Has a guaranteed disable for one or more of their spells."
Disablers are Heroes whose abilities are more focused to reliable crowd control, whether by single target or by area. Though fundamentally Support, they can act as Initiator in a gank when the number of enemy Heroes to be killed is few in number - a true Initiator's cooldowns are best saved for a large confrontation. They often lane with the team's carry to malign any attempts on their life. Disablers tend to have low base movement speed.
Gankers are Heroes with abilities that deliver long duration crowd control and/or immense damage in the early and midgame. They tend to have good mobility and rely on a mixture of physical and magical damage as well as disables to bring down their enemies. Their goal is to give the team an early game advantage during the laning phase by killing enemy heroes in their proper lanes. The Ganker role is often synonymous with the Semi-Carry role, as most Gankers become Semi-Carries if they are successful in their efforts, owing to a large gold and level advantage. However, because their abilities do not scale as well, they will usually suffer more in the late game (hence the need for a Hard Carry). Nevertheless, if a Ganker performs extremely well, he or she might prove to be the overall bigger threat to the enemy team at the game's conclusion than an allied Hard Carry. The most important task for a Ganker is to restrict the farm and levels of the opposing Carry.
Nukers are Heroes with fast, strong, and/or sustainable spell or magical damage output, whether it be through single-target spells or area-of-effect ones. Because area of effect damage comes mainly from nukes, Nukers can provide a huge damage-per-second advantage in team fights when they can harm multiple enemy heroes all at once. Area of effect nukers also excel at pushing as they can dispatch enemy creeps efficiently. Burst damage nukers such as Lina can also be deadly, as one single fast combo of her spells can often kill or grievously wound an enemy hero immediately before any reaction, thereby making a teamfight one-sided from the start. The mana cost and cooldowns of nukes often dictate how they will be used, as ones with low mana cost and/or cooldown can be spammed in lanes or in ganks, while ones with higher mana cost and cooldown are often best saved for large confrontations.
"Good at starting a teamfight."
Initiators are heroes who can safely and advantageously start a team fight. These heroes typically have strong area of effect damage or disable or some skill to affect the positioning of the enemy team. Many of these heroes rely completely on a positional item such as Blink Dagger or Force Staff to get the proper positioning to initiate a teamfight, while a select few, such as Elder Titan and Silencer, do not require this asset. Although it is common for an Initiator to be a Durable hero, this is not always the case; fragile heroes such as Enigma and Vengeful Spirit are adept at initiation.
"Can farm effectively from neutral creeps inside the jungle early in the game."
Junglers are heroes that can efficiently jungle neutrals at the start of the game, rather than lane. This allows for there to be two solo lanes, which in turn allows two allies to benefit from solo farm instead of one. Junglers typically have skills that allow them to convert neutral creeps, summon minions, or sustain themselves through moderate damage from jungle creeps; and the ability to Jungle is found in Heroes of all attribute classes and roles.
Although having two solo lanes and a Jungler produces a significant gold and experience advantage, it increases exposure to enemy ganks and can make side lanes weaker.
"Can quickly siege and destroy towers and barracks"
Pushers are heroes who focus on bringing down towers quickly, thereby acquiring map control. If they succeed, they often shut down the enemy carry by forcing them away from farming areas. They typically have skills that fortify allied creep waves, harm multiple enemy creeps and/or heroes at once, summon minions, or deal massive amounts of damage to enemy towers.
"Can focus on moving around the map instead of farming creeps early in the game."
The main goal of Roamers is to gain as much map control as possible early in the game by warding, ganking and studying the location of missing Heroes. They are also responsible for creep pulling, creep stacking (for the purpose of helping a fellow Jungler or to be the source of farm) and most crucially shutting down enemy Junglers. They often attempt to gank the enemy's mid hero, a difficult feat (albeit a very rewarding one) which usually requires a long-range disables and/or a Smoke of Deceit.
"Has the ability to last longer in teamfights."
Durable heroes (or "Tanks") are heroes who have the potential to sustain large amount of incoming damage from the enemy. They tend to have large amounts of HP, HP regeneration, armor, or magic resistance. They often have abilities to mitigate damage, avoid damage completely, or disable assailants. Strength heroes almost invariably perform this role because their primary attribute, Strength, also grants HP.
Despite the fact that most Durable heroes in Dota 2 cannot literally force enemies to attack targets (only Axe, Legion Commander, and Auroth may do this), they effectively play the role of absorbing most enemy damage output in a teamfight. This is accomplished by:
- Outputting an AoE effect which severely maligns the enemy, so that the enemy practically must kill the durable first; for example Undying's Flesh Golem which increases all damage to hostile units in its radius.
- Being the first one to engage the enemy in a teamfight. The enemy will respond by unloading abilities and items on the durable because a) the enemy cannot see the durable's allies and is tricked to believe the durable is alone for easy kill b) the enemy cannot reach the durable's allies because they are too far away c) the enemy is inexperienced and prematurely attacks the first hostile target in sight. The result is that the durable will probably survive because of his high durability; when the allies charge in, most of the enemy's skills are on cooldown and the battle becomes much more favorable. This tactic will not always work against seasoned opponents, however.
- Using an ability to force enemies to attack the Durable rather than his or her allies. The only examples of this currently in-game are Axe and Legion Commander, although Winter Wyvern also possesses a similar ability.
- Being the only target that can be readily attacked; a strategy that works best when the Durable's allies are ranged heroes.
In summary, a durable in Dota 2 is a durable hero with high survivability who often initiates a team battle and ideally is able to manipulate the enemy's damage output.
 Other Roles
Escape heroes are heroes equipped with one or more escape mechanisms which allow them (or sometimes their allies) to avoid damage and abilities while retreating or repositioning themselves during a teamfight or gank. Escape heroes are particularly suited to soloing the "suicide lane" or short lane, as they can turn situations where death is inevitable into a temporary delay in farm. Escape mechanisms include movement speed buffs, invisibility, teleportation (such as Blinking), and evasion. Many carry heroes also have escape mechanisms to give them the survivability they need to continue farming and killing.
Semi-Carries are heroes with strong early or middle game power that drop off later in the game; their name is derived from the fact that they "carry" for about half of the game. Their power decline can be due to poor farming ability, low stat gain, low mobility, non-scaling abilities, a lack of escape mechanisms, or any combination of the previous. The Semi-Carry, although long acknowledged in the community, is not a role recognized by Valve, likely because of the high ambiguity in defining the role.
Early on, the Semi-Carries typically take the lead in asserting map control to allow the Carry to farm. A Semi-Carry will often take the middle lane, allowing them access to both side lanes. A team typically has one or two Semi-Carries, depending on the laning strategy. If there is a Jungler, expect to see a Semi-Carry solo in the long lane (bottom for Radiant and top for Dire). A Semi-Carry will take the mid lane most of the time.
By the end of the middle game period, Semi-Carries transition into a more supportive role. This is not to say that they play Support; this is simply the point where their damage and capabilities are outstripped by "hard" Carries. To amend their damage "falling off" (as it is called), they often build items such as Basher and Scythe of Vyse to replace their ailing damage output with some utility instead.
"Can focus less on amassing gold and items, and more on using their abilities to gain an advantage for the team."
Supports are heroes whose purpose is to keep their allies alive and give them opportunities to earn more gold and experience. Supports will usually come with skills, such as healing spells or skills that disable enemies; and generally have low damage output (but often with a powerful-yet-situational ultimate). Like Semi-Carries, Supports are not dependent on items (with some exceptions such as Windranger and Necrophos), and thus, much of their gold will be spent on items for the benefit of the team such as Animal Courier, Observer Ward, Sentry Ward, and Smoke of Deceit.
Supports are typically paired with the team's Carry at the start of a game. This is because the Carry tends to be the weakest and most gold-hungry member of the team early on, whereas support heroes are at their strongest in the early game. A Support should always forfeit kills to any teammates who are more reliant on items than she/he is, only performing a kill if none of his/her allies are able to do it.
Offlane heroes are those with skills that allow them to solo the "suicide lane" (top lane for radiant, bottom lane for dire). Having an offlaner in a team's lineup allows the team to also have a jungler or run a tri-lane with less risk of losing the suicide lane to the opposing lane. In many cases, the offlaner may have to forgoe a great deal of farm in order to simply stay alive, and as such may be on the back foot much of the time. Heroes with the ability to escape from certain death are best suited to this role, as the offlaner's first priority should be to not die in lane. Against skilled opponents, the offlaner may be extremely under-leveled compared to other heroes on the field, and as such it is generally unwise to put a hard carry in the offlane because they may not get enough farm to obtain the items they need to snowball into the late-game.
Generally speaking, heroes that can excel in the offlane and still be effective throughout the game have at least one of these qualities:
- A skillset that allows them to escape from ganks safely. See Escape.
- They are able to secure a reasonable amount of farm despite the possibility of being forced out of lane.
- They have abilities that will keep them alive in the early-game as well as allowing them to be effective in the mid-game despite a lack of gold. Supports such as Tidehunter and Windranger are examples of this. This can include heroes whose skills have a great deal of utility later on in the game. For instance, skills like Mirana's Moonlight Shadow and Earth Spirit's Boulder Smash can serve to benefit other teammates as well as the player in a variety of scenarios.
- They are able to disrupt the enemy carry's farm. Good use of summons like Lone Druid's Spirit Bear can position friendly creeps in a place where the carry may struggle to get last hits, such as under a friendly tower from where you can deny them safely.