Bowser

Bowser...the King of the Koopas
A huge Koopa, with a green, spiky shell, red fur, a long tail, claws, and a physique that makes his maids swoon. And with the ability to breathe fire like a dragon.
Serious, powerful, calculating, and with a talent for singing and playing the piano, his henchmen describe him as...intimidating, which is why none of them dare to even confront him. Although his plans to conquer the Mushroom Kingdom and marry Princess Peach never go well thanks to Mario, despite his immense strength and ability to throw fire, troops, and armies.
Although he doesn't show it, Bowser is a very doting father to his children, and sometimes they help him against Mario, but it doesn't usually turn out well. Oh, and Bowser has already given up on marrying Princess Peach; he never manages to do it anyway.
He harbors a great grudge against Mario, which further fuels their rivalry, but Bowser never gives up and continues with the same formula of kidnapping Peach, poor guy.
Bowser has had few encounters with Sonic and his universe, but he knows more or less that if Mario defeats him, Mario and Sonic together will rather bury him, but he is interested in that universe.

Bowser is the father of Bowser Jr. and the Koopalings. He is a present father, and his children sometimes help him in his plans against Mario (and they love him very much :D).
Bowser was raised by Kamek, a sorcerer who later became his henchman, although deep down he harbored a certain affection for him.
His love for Princess Peach (Queen of the Mushroom Kingdom) has begun to fade, he hates Mario, and incidentally, Mario is the cause of his plans to marry or have something with Peach.
He has a huge army of Soldiers, Koopas, and many more, and his goal is to destroy Mario and conquer all the kingdoms of this world...
He doesn't know much about other universes besides his own, but he is aware of them; sometimes he saw Sonic team up with Mario, but not regularly.