Lembit Opik was first elected to the Commons in 1997 to represent Montgomeryshire.
One of the more colourful characters on the Liberal Democrat benches, he is known for his harmonica playing and his campaigns to alert Parliament to the dangers of meteorites.
He also holds a private pilot's licence and has been known to fly former party leader Charles Kennedy to party engagements.
He was a councillor in Newcastle-upon-Tyne and contested the Newcastle Central seat in the 1992 election.
Mr Opik has been leader of the Welsh Liberal Democrat Party since 2001. But he was defeated in his bid to become Lib Dem party president in 2004 by Simon Hughes.
Mr Opik was the only high-profile backer of former home affairs spokesman Mark Oaten's short-lived campaign to become party leader.