Bowser is the main antagonist of the Mario series.
Super Mario Bros.Edit
Bowser is fought at every castle level in the game. He spits fireballs at you. When you hit the switch, the bridge he stands on will collapse and he will fall in the lava. After the fight, Toad will tell you that Princess Peach is in another castle until the final castle where Peach will thank you.
Super Mario Bros. The Lost LevelsEdit
Just like in the first game, Bowser is fought at every castle the same way.
Super Mario Bros. 3Edit
Bowser is the final boss.
Super Mario WorldEdit
Bowser is fought on the roof of his castle in his Koopa Clown Car. He throws Mecha-Koopas at you.
Super Mario 64Edit
Bowser is fought 3 times.
In the Dark World, you defeat Bowser by throwing him into a bomb.
It is a little tougher because Bowser tilts the platform but you could still throw him into the bomb.
The final fight is the toughest. You now have to throw him to the bomb three times and he breaks the platform in the shape of a star.