Angelus

Angelus was a construct created by an Asuran biomass known as the hybrid. After the hybrid escaped an attempted destruction by the Asurans, it created Angelus to infiltrate Atlantis, using Doctor Elizabeth Weir's memories to mold him into what it needed. Angelus had no idea of his true nature and believed he was an Ancient who had a family, but who's planet ended up destroyed. Angelus helped with the creation of a "weapon," unaware of his true purpose and ended up absorbed by the hybrid. Despite being absorbed, Angelus' conciousness survived and after Sheppard stunned the hybrid by ramming it with a Puddle Jumper, Angelus managed to gain some control over its basic functions. He created a sort of body for himself and saved Sheppard by cushoning his fall. Angelus was horrified by the truth of what he was and knew the hybrid had to be killed so he teamed up with Sheppard to do it. After gaining Sheppard's trust, Angelus took over two litters of Sheppard's blood and used that and Sheppard's ATA gene to manufacture a poison to kill the hybrid while it was stunned, using its ability to create whatever it needed. Angelus helped Sheppard escape, but lost control at the last moment as the hybrid woke up. However, Sheppard was close enough to the edge of the hybrid that he escaped on his own. The hybrid died of the poision and Angelus died with it.