I can't believe no one has said it yet: "Who is Tyler Durden?"

Anyway, I was in (for a brief time) a 2nd edition game where one of the players was a giant with multiple personalities.
He'd chose an axis of alignment, good, evil, lawful, chaotic, Neutral (on good/evil) or Neutral (on law/chaos). Then at the start of each day, he'd roll a dice. And what number came up, dictated his alignment.
In his case, he was 'lawful' So each day, he'd be either lawful good, lawful neutral, or lawful evil.
He also had 3 specific triggers. Each trigger would force him to a particular alignment, regardless of what he rolled that morning. Ex: Taking bludgeoning damage while within a darkness spell forced him to lawful evil.