Originally posted by Blight
I know, but Generally the idea is that the "bad guy" of a comic book is the "antagonist". Deathstroke is the "Protagonist" of his own comic, making him in direct opposition to the "Bad Guy".He's always been a mercenary, but he hasn't always been a badguy.
A protagonist is just the main characters of a story, traditionally they're the "good guys" but not always. There's such a thing as villain protagonists, e.g., Thanos in Thanos Quest. He was definitely a bad guy, but he was still the protagonist, and the antagonists were the Elders (some good, some bad).
Deathstroke can be seen either way (good or bad), but the role he takes usually depends on which ever brings in the bigger paycheck. And usually it pays more to be a bad guy especially if the main thing you're selling is murder.