Clarke Griffin is a major character in the first, second, third, fourth, and fifth seasons. She is portrayed by Eliza Taylor. Clarke debuts in the Pilot.
She was locked up in the Sky Box after her father discovered a problem with The Ark's air supply. He had plans to go public with this revelation, but before he could he was arrested and floated. Clarke knew about his plans and was going to release them herself. She believed the people had a right to know. However, she was sent to Lockup before that, and became Prisoner 319.
Clarke is shown to be a natural born leader, and co-leads the 100 with Bellamy Blake when they arrive on the ground. She keeps him from letting all hell break loose, and together they establish rules and a system of survival. Because she was a med student, she's also the primary doctor once they get to the ground. She tries to negotiate a peace treaty with the Grounders, and helps lead the defense army against them when they attempt to attack their camp.
She allows 300 grounders to burn because of this, and is taken by the Mountain Men after successfully defending the camp.
Clarke had a good childhood. Her parents were both well respected members on the Ark, and they were good friends with Thelonious Jaha, the chancellor. Wells Jaha was Clarke's best friend.