Lord Willoughby was the main antagonist of the Gummi Bears episode "He Who Laughs Last" - at first little more than a bad-tempered and arrogant jerk with a dislike of Sir Garwin and his stories involving Gummi Bears he became more malicious when he believed that Garwin was making fun of him.
Lord Willoughby tried to get King Gregor to punish Garwin out of spite, accusing the retired knight of being a "menace" - however King Gregor rightfully told Lord Willoughby that Garwin was just a harmless old man with a love for stories and refused to punish him for simple story-telling.
This infuriated Lord Willoughby and he became determined to humilate Sir Garwin, challenging him to find real proof that Gummi Bears existed, a challenge Sir Garwin had little choice but to accept due to the honor system knights followed (even in retirement).
Lord Willoughby forced Sir Garwin to bet his entire fortune on the existence of Gummi Bears, leaving Cavin with a moral dileem as he was torn between seeing his grandfather become peniless over a silly rivalry or losing the trust of the Gummi Bears.
Ultimately Lord Willoughby himself was captured by the Gummi Bears after Lord Willoughby stole the Gummi Medallion, which Zumi had dropped during a rescue attempt when Tummi ate a cursed fruit: however the curse could not be lifted without the Medallion.
Although facing the prospect of being peniless Garwin promised the Gummi Bears he would not tell Willoughby of their existence after all and would get their Medallion back - Gruffi was still distrustful and thus Zumi offered to go with Sir Garwin to ensure the Medallion was brought back safely.
Meanwhile Cavin, having suspected foul play by Lord Willoughby, snuck into his room at night and found the stolen Medallion - however Lord Willoughby caught Cavin and locked him in a closet to prevent him from warning anyone and told him he would "deal" with him and his grandfather soon enough.
Later that night however Garwin and Zumi also sneak into the room and take the Medallion, awakening Lord Willoughby again - despite being a thief himself Willoughby is brazen enough to accuse Garwin of being a crook and yells on the casle guards to seize him but both he and Zumi escape.
Yet Lord Willoughby pursues them into the forest, once again fuelled into a rage when Garwin somewhat cheekily calls him "chubby" - riding on horseback he chases them until Garwin tells Zumi to go on while he confronts the mad aristocrat.
However Lord Willoughby is too quick for either and promptly steals the Medallion once more, mocking Garwin as he rides back towards the village - by this time the other Gummi Bears were aware of what was happening and stop Willoughby, confronting the now cowardly villain as he flees from the bears: afraid they would harm him (even though Gummi Bears are largely harmless creatures).
Lord Willoughby continues to flee until he comes across Garwin once more and in a panic tells him the Gummi Bears are attacking him - in a clever twist Garwin pretends not to believe Willoughby and the villain is left a bumbling wreck as he tries in vain to prove that he was telling the truth.
In the end Willoughby is utterly humilated and calls off the bet, in his final appearance he is seen as a cowardly fool still trying desperately to convince people the Gummi Bears were real - eventually being escorted out the tavern by guards as he babbles on about the "furry monsters".