Abraxas is a little confusing, like many of these people. What happened to characters who drank a super serum and got their powers? All these galactic beings have such weird backstories. Abraxas is an evil, strong dude who was born within another dude named Eternity. The only reason he couldn't go 'Sling Blade' on people was because Galactus could put him in check, but after Galactus died, Abraxas popped off. He threw Galactus' head at Earth. That started a whole thing with the Fantastic Four.
The Fantastic Four teamed up with Silver Surfer and some other people and ended up defeating him by resetting reality, or something like that (it's all made up science. Regular science is hard enough, don't make me learn made up science). After reality was reset, Abraxas wasn't there anymore. Moment of silence for Abraxas.