Sigma

Sigma was a fragment of an artificial intelligence program developed for the Special Operations program Freelancer during the Human-Covenant War, originally assigned to the Freelancer Agent Carolina, but after Agent Maine was injured she differed it to him so he could still communicate with others. It was one of many fragment constructs that were born from the degradation of the original Alpha AI, splitting off Alpha's creativity, as explained by Freelancer Washington. Sigma was the creative/ambition of the Alpha AI.

Sigma was behind The Meta's rampage to kill fellow Freelancers and steal their A.I. and equipment. Sigma believed that if it brought together the A.I. fragments then he would become the Alpha, however this ultimately didn't happen since Sigma, along with all the other A.I.s captured by The Meta were destroyed in the EMP. His intentions if he had been given the chance to become the Alpha remain unknown.