He joined Marian's band after she took him hostage and threatened the Sheriff that she would burn King John's new underpants.
After Little Ron joined the gang, they set off to find Barrington and Rabies who are being tortured at King John's Castle. They arrive dressed in hoods and after freeing the two men and tying King John and the Sheriff up, Robin removes his hood and burns King John's underpants where Marian whispers "Robin...Hood" which is how he got his name making him hated and feared by King John and making him out to be the leader of the gang.
Even though Marian was the leader who formed the band, Robin inadvertantly got all the credit, but thought that this was a great image to cultivate. He was highly praised by the people at Worksop and his biggest fan was Rose Scargill who constantly collected everything that Robin either had walked on, touched or wore.
He is sometimes portrayed as being quite vain and selfish, such as when he spend all the merry men's pocket money on a new white suit which eventually ended up ruined after he fell in a giant mud puddle.
Even though he is a bit of a coward and gets scared very easily, he is always ready to help when needed. His main attributes to the gang were their lincoln green outfits blending in with the colour of the trees and his cow horn. He is all heart and often comes on top in the end.