Spoiler for players.
[sblock]In adventure 5, the party encounters a minotaur that Pilus biomantically combined with an air elemental to make a devastating defender for his laboratory. If you want to tie the player in, you could have a small nation of minotaurs - maybe a few different tribes - living in the mountains between Ostalin and Sindaire. Perhaps the PC is from there; it's up to you and your player as to how he made it to Gate Pass.
Then when the party gets to the monastery, you could add a sub-plot about the local minotaurs being abducted. Maybe Aurus, the half-air-elemental minotaur, betrayed his village and is working for Pilus to bring him samples.
Alternately, since minotaurs are sort of half-man half-beast already, you could say that as a race they were created by Pilus, or perhaps an earlier biomancer, whose research Pilus used as the basis for his creations. If your player is going against type and being an arcane class, you could even give the minotaur PC access to a few biomantic style bonus powers or rituals, and set Pilus up as an antagonist for him.
Oh, and um, a minotaur shows up in the art of one of the big battles in adventure 4.
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