“The Gnostics were divided in their opinions concerning the Demiurgus, or creator of the lower worlds. He established the terrestrial universe with the aid of six sons, or emanations (possibly the planetary Angels) which he formed out of, and yet within, Himself. As stated before, the Demiurgus was individualized as the lowest creation out of the substance called pleroma. One group of the Gnostics was of the opinion that the Demiurgus was the cause of all misery and was an evil creature, who by building this lower world had separated the souls of men from truth by encasing them in mortal vehicles. The other sect viewed the Demiurgus as being divinely inspired and merely fullilling the dictates of the invisible Lord. … To the Gnostics, the Christ was the personification of Nous, the Divine Mind, and emanated from the higher spiritual Aeons. He descended into the body of Jesus at the baptism and left it again before the crucifixion.” ~Manly P. Hall
I don’t think the beliefs of various Gnostic groups differed as much as Hall indicates. I think it is his interpretation that makes it seem that way. In any case, they did agree on most important aspects of the creation of the material realm and on who created it.
The Demiurgus, as Hall calls him, more commonly called Demiurge today, is considered the creator of the material worlds or the material dimensions of existance according to gnostic teachings. It is not clear who this being (or beings) is, but most likely it is another name for Lucifer and the other fallen angels. These angels let their desire to be more like God take control of them and convince them to create their own realm where they would be worshipped as gods. They did not realize that they did not have the full powers of creation that God has and so the realm they created, the universe of matter, was not true creation but was made by altering the spiritual, by making it slower and distorting it. In a sense, they created a distorted, fun house mirror image of the real worlds of spirit. And this is the world we live in.
In one Gnostic version of the creation of man, the Demiuge created man as a simple animal, but God took pity on us and gave them souls so they could return to heaven one day. In the other version, spiritual beings choose to descend into matter to experience what it was like, kind of like kids playing in mud, and after time forgot who they really were and how to return to their true selves. These two variations are probably both allegory and the truth lies somewhere between.
I think that all groups of Gnostics blamed the Demiurge for the miseries of the world, at least in part. Obviously, the creator of a realm in which everything grows old and dies, get diseases, and must kill other living beings and eat them to survive, is responsible for most, if not all the misery of this place. We do contribute to it, of course, by giving in to our fears and nursing them instead of fighting them, and by believing there is noting else, no spiritual worlds, so we must embrace the material no matter how flawed and how full of horrors it is. We can reduce the misery to some degree by not accepting that death, disease, and killing is normal.
To all Gnostics, Christ was not a person, but a Divine Spirit. He was the first creation of the true God, and therefore the true son of God. But while the spirit of Christ dwelled for some time in the Body of the man Jesus, Jesus and Christ are not one and the same. Jesus was Christ, but Christ was not always Jesus, and is not today. Christ was also in other great spiritual leaders of the past. Today, Christ can be found in the Sun of Righteousness, which is not another name for Jesus. When Jesus said he would come a second time, he was speaking as the spirit Christ, and not the man Jesus. Christ has returned, Jesus has not, although, of course, Jesus is not dead and is working with other great spiritual beings from the other side to help fulfill God’s Plan for the Earth, which is to return it to the worlds of spirit.
It is true that Gnostics believe that when Jesus was baptised and, as the standard Bible puts it, the Holy Spirit descended to him, that at that moment the Christ spirit entered him. I don’t think it is true that Christ left Jesus before the crucifixion as some of the things Jesus said on the cross indicate that he was still sometimes speaking as Christ.
In any case, the important teaching of all Gnostic groups is that we must all take an active role in awakening our spirits and souls in order to regain our true selves and have access to the divine wisdom and knowledge tat come from heaven.