In the Mage version of the story, Tremere was experimenting with vampiric blood and accidentally became a vampire.

Mage the Ascension didn’t come out until 1993 and most of the rotes that could be used for immortality came out in expansions. The first edition of Vampire the Masquerade came out in 1991. In the Mage: The Ascension supplement Blood Treachery, Tremere claims to have known his Avatar would die upon performing the ritual that transformed him into a vampire. What happens to the members of House Tremere?.What’s the difference between a Tremere and a vampire?.Who are the tremeres in Vampire The Masquerade?.