Alpha in Epitaph...

It is subjective. It's suddenly to us, but to the characters, there's a ten year gap.

I can only imagine the story arc that changed Alpha from number one enemy to ally. He even seemed sad when he learned of Paul's death, which to me implies they'd also gotten close over the years.

I believe he took a similar journey to Echo. He started becoming more self aware and the better personalities started having more influence over the criminal ones. Echo probably helped guide him. Sort of like how Angel guided Faith.

Straightedge means I'm better than you.

I read somewhere that after imprinting himself with Paul Ballad's personality might have been an influence on Alpha.

If it's all the same to you, I'll have that drink now.-Loki (Marvel's Avengers)

In the graphic novels Alpha explains that the Paul Ballard imprint he gave himself was the catalyst for his reformation and newfound ability to control (for the most part) his psycho imprints.

Alpha like Echo, is able to "hold multiple people all at once. However because Alphas first self, as Ballard puts it "their soul" is still there. When the imprints were all dumped into Alpha they brought him back to his original self which was a serial killer. Alpha became Carl Craft who liked to kill people. Adele got Craft from prison to experiment with imprints.