The Source is the double of Earth CA’s Adam Halliwell but on Earth CB, which is a duplicate of Earth CA. On Earth CB, Charmed One Prue Halliwell was killed by the demon Shax. He is the son of Charmed One Phoebe Halliwell and the demon Cole Turner. He was created by them originally to rule the underworld as the Source. When Phoebe returned to the side of good, the Source was for a time “dead” until Adam Halliwell was able to convince Phoebe to let the Source live to save existence from being destroyed by the "Inconsistency". To save existence, he had to save Prue in that Adam’s reality and that Adam kill Prue in this Adam’s reality.
There is most likely no way to vanquish or kill him and is immune to all magic. His powers appear to be unlimited as he appears to have the magic powers of every magical being from Whitelighters to Witches to Demons to any magical life form imaginable.
Although he is not the original but the third Source and only a few years old, all the memories and crimes of his predecessors were passed on to him. Despite, the number of demons in Earth P (Beta Morphin Grid), the only demon to know of his power and existence is Queen Bansheera.
Today, he is Earth CB’s “good” Source of All Evil and uses his powers to protect some members of his family. He later came to Earth A with Adam Halliwell/Electro and both joined the Justice League, him being the third recruit, after they helped them fight the warlock Darco.
