In 2267, a sour, suspicious old man, he immediately questioned the USS Enterprise landing party's motives for retreating from the Festival. When Tamar tried to calm the waters, he took the comments for mockery of the lawgivers, and fled Reger's house.
The next morning, he returned with lawgivers, having evidently convinced them matters at Reger's house required their attention. Acting on Hacom's accusations, the lawgivers murdered Tamar and demanded the Enterprise landing party accompany them to the absorption chamber. When Kirk's disobedience forced the lawgivers to commune with Landru, Hacom fled the house. (TOS: "The Return of the Archons")