Bowser is portrayed as the "King of the Koopas", anthropomorphic turtles that inhabit the world of the Mushroom Kingdom. Bowser differs greatly from the rest of the Koopa clan, which consists mainly of bipedal tortoises. He is characterized by a large, spiked turtle shell, horns, a draconic muzzle, razor-sharp fangs, taloned fingers, three clawed toes on each foot, red eyes and a shock of red hair.

He is physically endowed with immense strength, is nearly indestructible, and can breathe fire. He can also jump surprisingly high for his large size, although his speed and agility are most of the time lacking. He is also accomplished in black magic, thanks to which he can teleport himself or summon objects, fly, generate a huge amount of electricity, use telekinesis or metamorphose.