The term "caller" usually refers to one of two roles a in a GvG team: a strategy caller or a spike caller. Often these two roles are filled by the same person, but it is not necessarily so. Callers are often placed in position one in a team as the team leader but can be in other positions in order to mislead the enemy team.
Similarly, PvE (especially high-end PvE) often has someone acting as a caller.
A strategy caller is a team member who acts as strategist and leader during a match. The caller will designate targets, manage team positioning (whether to advance or retreat), split the team into groups, and make other strategic decisions. Inexperienced teams will rely heavily upon their caller who will often have to micromanage several members of the team.
This model used to be very common, but modern playstyle has developed such that every member of a team is expected to make calls at both the tactical and strategic level and act independently, the role of a caller in experienced teams has shifted more towards calling a majority of the strategy and acting as a final decision maker when conflicting calls are being made by various team members.
The caller is often a frontliner in a balanced build.
Sometimes various calling responsibilities will be given to different members of the team, for example in a GvG the flag runner may be responsible for calls which coordinate split play. The importance of designating specific callers arises from the fact that often following an incorrect call in a coordinated manner can have a better effect than a team acting in two conflicting manners, even if half the team is acting appropriately.
A spike caller purely exists to coordinate damage in time and target. In a build that includes melee characters one of them will often be the caller due to the positioning requirements of melee and the difficulty in determining when someone else's adrenaline-based skills are recharged.
Typically a target will be called and depending on the build a countdown will start, usually over voice communication software such as Ventrilo or Teamspeak, with each team member who is involved in the spike switching to the target and activating their damage skill at a time related to the cast times of their spike assist skill.
Some builds contain multiple spike callers due to the recharge time of various spike skills, in this case it is important that the two spike callers do not overcall each other by calling spikes during the each other's calls.
 PvE caller
Similarly to spike callers in GvG, callers in PvE call out a certain foe but differenciates in that it's not for spiking. PvE callers, usually filled by the support or utility team members, are the individuals in the team which set up priority targets. In most cases, these will be either enemy support (Monks, some Ritualists, and Paragons) or high damage dealers (such as Assassins and Elementalists). When dealing with high-health bosses, they are also used to alert the team to any new weaker foes which should be dealt with instead of continuing to drain the boss' high health, in order to reduce pressure on the team.
|Team roles and builds|
|Damage||Pressure • Spiker • Nuker||Beast master • Bomber • Dagger spammer • Touch ranger • Trapper|
|Support||Healer • Protection||Battery • Bonder • Imbagon • Infuser • Orders|
|Control||Lineback • Shutdown • Tank||Cripshot • Hexway • Minion master • Spirit spammer|
|Utility||Caller • Toolbox|