Digimon Masters

Not much is known about the "Digimon Masters" only that one of them says that the Protagonist was originally chosen as a Tamer by mistake, and the Wise Digimon says to him, "There are no accidents."

Speculation
It is probable that the "Digimon Masters" are the rulers of the Digital World in Digimon World Alpha, and likely take a similar role to that of the Digimon Sovereign in the Tamers Anime series.