Bill Mulder first appeared in Colony, a flinty, unsmiling and remote man. He reacts to his son´s, Fox Mulder´s, attempts to hug him by putting him off with a handhake. In End Game, when Fox must tell him that Samantha is lost again, Bill Mulder turns his rage and pain outwards to his son, and even though his son´s suffering is obvious, he maintains his icy reserve. A conversation with the Cigarette Smoking Man in Anasazi reveals the two to be on first-name terms. These two men worked together on a secret project whose exposure they now fear, and we discover that Bill Mulder is a troubled, deeply quilt-ridden man, terrified that Fox will found out about his involvement. As his conscience finally drives him to confess his role in the secret cover-up to his son, Alex Krycek assassinates him as he is on the point of disclosure. Taking his last breaths in Fox´s arms, his final words are a plea for forgiveness.