caller, n. 1. in tabletop RPGs, a player given the task of determining what actions the other players wish the character party to make, and then presenting this information ("calling the turns") to the GM; often, the caller is the player whose character is the leader of the party. 2. the player whose character is the leader of the character party. Also party leader. [GJ1]
Addendum: Assigning a caller is particularly useful to a GM who is running a large game, one with seven or more players. The caller takes on the task of focusing the group's attention and quizzing players for clarification, leaving the GM free to pursue recordkeeping chores and resolve individual problems. Some GMs give the caller a great deal of authority over the other players, taking turns only from the caller and siding with the caller in disputes with players. [GJ1]