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.