Sir Rothbart (Also known as Lord Rothbart, The Great Animal or just Rothbart for short) is the central antagonist in The Swan Princess franchise, serving as the primary antagonist in the first and fourth films and as a posthumous antagonist in the second, third and fifth films. He is a court warlock who changed Princess Odette into a Swan. In Tchaikovski's ballet, the sorcerer is called Von Rothbart and he transforms the actual princess into a swan, planning to have his own daughter marry the prince.
In the animated movie loosely adapted from the ballet, he is a vile and greedy court warlock who plans to get rid of the princess and her family to take over the kingdom.
Biography
Rothbart and the evil magician Clavius conquered the Forbidden Arts (Rothbart's magic power) together, but Rothbart betrayed Clavius and drove him underground, as revealed in The Swan Princess 2.
He planned to take King William's kingdom with his magic power, but as he was about to attack, William's men attacked him and took away his power. Despite calls for his death, William banished him instead. He left swearing that he would get his power back and take over the kingdom.
Many years later, he returned, having gotten his power back (in The Swan Princess 3 it's revealed that Zelda helped him regain his power and he betrayed her afterward, similar). He transformed himself into a monster known only as "The Great Animal" and assassinated William before placing his daughter Odette under a spell, turning her into a swan every day, and she can only turn back into a human if she is on the lake when the moonlight touches it. Every night Rothbart asked Odette to marry him so he can be king, but she refused.
When Prince Derek finally found her, he resolved to break the spell, which could only be broken by making a vow of everlasting love and proving it to the world. To prevent this, Rothbart transformed his servant, Bridget the hag, into Odette so that Derek would make his vow to her instead, as this would kill Odette. Also there was no moon at the night of the ball in which Derek intended to make this vow. His plan succeeded, but Derek told him to not let her die, and so he transformed into the Great Animal and fought Derek, crushing his sword in his mouth. Jean-Bob the frog gave Derek his bow, and Brom shot an arrow to him. Being a pro at "Catch and Fire", he caught the arrow and shot Rothbart in the heart, killing him and sending him falling into the lake, exploding in a flash of magic lights.