Thomas Cahill was born to Gideon Cahill, and Olivia Cahill. Thomas loved his sister Katherine Cahill, and they'd go on walks together. The only issue was that he didn't fully trust her. Their father gave them a fourth of a serum to combat the plague, and the clues on how to make the serum. Thomas suffered a side-effect where his DNA gave him more fighting skills than ever. He had a great relationship with Katherine, and when Gideon was killed, he banded with her. They tried to escape Europe to leave the influence of Luke Cahill, their brother, suspected of killing Gideon.
In Portugal, Thomas met a girl and married her. Katherine disapproved, but they lived for three years. Wary of Katherine, Thomas stole all but one of his clues from his hiding place. He left a note, pleading Katherine not to follow her plan. One day Thomas woke up to find that Clue and Katherine gone. He tracked her down to a ship departing for Egypt, and tried to tackle her. Katherine outwitted him.
Thomas and his wife continued searching for Katherine, and in Japan had the first Tomas, Toyotomi Hideyoshi. He became the first Tomas, and Thomas died in Japan, with only his wife and son.