Sinsear was a man in Cable's future. He was mortally injured in an explosion and was found by Cable and his Clan Chosen mates. Unlike many enemies that carry grudges for pain actually inflicted, Sinsear held his grudge because Cable would not end Sinsear's life. Instead, Cable merely alerted Sinsear's allies, an act that got the man the attention he needed, but would also painfully transform him into the one-man army who would be credited with killing thousands upon thousands.
Once a cyborg, Sinsear went through various forms of training and tests before he was given his main duty. He was instructed to travel to the present and kill two timetravellers. The first was
, who had taken on the name of Tolliver, an arms dealer. The second target was Cable. Upon arriving in the present and learning that Cable was Tyler's father, he changed his programming and went after Cable first. He phased Cable to a battle ground most favorable to Sinsear, but Cable ended up winning anyway. Sinsear, badly defeated, escaped back to the future without fulfilling his directives.