Conversation so far:
when do damon and elena get together in vampire diaries
In the episode My Brother's Keeper, Elena tells Damon he is the reason she and Stefan broke up and Damon and Elena finally have sex.
who plays Elena in The Vampire Diaries
Elena Gilbert is portrayed by Nina Dobrev.
who plays Damon in The Vampire Diaries
Damon Salvatore is portrayed by Ian Somerhalder.
what's Damon's role in the show The Vampire Diaries
Initially, Damon is the main antagonist with murderous and apathetic agendas.

Question: why is he the antagonist
Self-contained rewrite: why is Damon the antagonist in The Vampire Diaries