Tommy Oliver

Placed under a spell by Rita Repulsa, became the evil Green Ranger
After the spell was broken in a battle against the Rangers, he joined them
Lost his powers when Rita used the magic green candle, temporarily got them back
Granted the powers of the White Ranger by Zordon, became the leader of the team
Was given Zeo & later Turbot powers when his power coin was destroyed
Stepped down from being a ranger, got a doctorate in paleontology
Found dino gems, became the Black Dino ranger for a short time
Given the Master Morpher allowing him to access all his past Ranger powers
After years of fighting as a Ranger, he retired to focus on his family