So we have seen who Savitar is by now, but it makes no sense! Well i got a theory to clear up the mess and hopefully it is correct.
I believe Savitar is Flashpoint Barry.
As we know it, Barry saw that the timeline was going to hell during Flashpoint so he restored it to how it was. However what if there was another Barry that ignored Eobard on the fact that he was turning into the villain of the story? What if Barry stayed in Flashpoint? This is the version that i believe became Savitar. So how? Well you know how Barry started losing memories of his old life, so he did do this. However as he did, he decided to give himself superspeed since he forgot he had it and wanted to restore his powers, not knowing that he still had them. This doubled his speed, causing the white lightning. He had to contain this amount of power in a suit of armor which because he forgot he was the Flash, he became Savitar instead. The hero of Flashpoint earth. Discovering that his world was slowly breaking apart thanks to our Barry restoring the timeline, Savitar went to the main earth to take revenge on this Barry for destroying his world and taking everything from him.
Evidence points to this.
How Savitar said that Barry took everything from him when speaking through Julian.
Now there is one problem which is the fact that how does this Flashpoint Barry know about our Barry? Well he probably got memory flashes of the original timeline as he saw familiar faces as Dr. Alchemy and Savitar. After all, he saw Wally, Cisco, Caitlin, and HR over time. Also Savitar only adressed the Flash as Barry after seeing him for the second time when talking through Julian. So this was probably because he got his memory flashes around then.
Another piece of evidence is in the Speed Force. Why would it imprison Savitar if he was Barry? Well they did because this is a Barry who didn't rewrite Flashpoint. He deserved to be punished for that.
So that is my theory on why Barry is so evil. Leave your thoughts on it down below.