http://dota2.gamepedia.com/Roles(Source)

Role

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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.

Contents 1 Roles 1.1 Main Roles 1.2 Lane Support 1.3 Carry 1.4 Disabler 1.5 Ganker 1.6 Nuker 1.7 Initiator 1.8 Jungler 1.9 Pusher 1.10 Roamer 1.11 Durable 2 Other Roles 2.1 Escape 2.2 Semi-Carry 2.3 Support

Roles

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 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.

• Examples: Dazzle, Lich, Omniknight, Warlock.