In episode 6 of Game of Thrones season 1 Tyrion requests a trial by combat and asks for a champion. Some guy that I have no idea who he was volunteered and won. Who was that and where did he come from?
The champion was Bronn, he was in the tavern when lady Catelyn abducted him on behalf of all the bannerman and he was a mercenary in those troops.
On the ride to the Eyrie, they have a slight bonding moment and Bronn decides that allying himself with Tyrion would be more profitable due to him being a Lannister, and, I believe in secret, respect Tyrion's attitude towards life.
It was Bronn, a sellsword who took up as the Imp's champion for wealth. He met the Imp when Lady Catelyn was at The Inn at the Crossroads and called forth men to seize Tyrion. He fell in with the other Vale men for rewards, but grew close to the Imp during the journey to Eyrie.