In his interview with “Details” he is quoted saying: ‘Spider-Man was something we talked about. Batman was another one. But I somehow knew those roles had potential to define me, and I didn’t want that. I didn’t want to be labeled as Superman for the rest of my career. I was maybe 22, but I saw the danger.’
He did go on to explain that as a result of declining the roles, he ended up having issues with his agents.
He goes onto say: ‘I didn’t have those agents for much longer after that. There was a lot of infighting between my manager and agents, trying to figure out who to put the blame on. It got to the point where none of us were able to work together.’
At the time the roles went to rather different actors- Tobey Maguire played Spider-Man, Christian Bale took on Batman and Brandon Routh was Superman.
source: dailymail