A tamer is the human partner to the digimon. In Digimon Masters you take the role of a tamer. There are currently 4 tamers to pick from the start of the game.
The Digimon Adventures Tamers are currently avaliable only by drop at File Island Maps, or obtained at certain events.
Each tamer has different strengths and weaknessess. When choosing your digimon, take into account the tamer that best suits the strength of your digimon.