Was he born with the scar or did he manifest it??

Fun fact

Before the incident that gave him his scar, the name that Scar's parents gave him was Taka. Which means "Trash".

So yeah, dude maybe had a little right to be vindictive.

Actually he was named Taka (meaning "waste" or "want" in Swahili) and took the name Scar later, because of his.. scar. Or Askari, the extended universe is contradictory on this.