Ludo was the main antagonist for most of season one, where he sought to claim Star's magic wand as his own to rule the universe, and briefly allied with Toffee to do so. By season two, he gains his own wand, but gets possessed by Toffee. At the beginning of season 3, he briefly conquers the Kingdom of Mewni. As of Star vs. the Forces of Evil: The Battle for Mewni, Toffee has been expelled from Ludo, while Ludo is currently on a soul-searching journey as part of his request to Star.
Ludo was once part of a family of bird-like creatures led by Lord Brudo and Lady Avarius in Mewni. He was considered the runt of fifty offspring and did not grow properly like the rest of his siblings; due to his abnormality, his family treated him severely in hopes of toughening him up for most of his childhood. When he was younger, Ludo became frightened of beards from a traumatic experience involving a beard during a birthday party.
One day, when the family went on a vacation without him, Ludo seized the opportunity to lock them outside and took over Castle Avarius, forcing his family to vacate to the Forest of Certain Death. Ludo then built an army of monsters over time and began organizing plans to steal the wand of Mewni's royal family.
Ludo is defined by his maliciousness and selfishness, bent on obtaining the magic wand to rule the entire universe out of pride without any qualms against who gets hurt in the way, even his allies. He has no empathy towards his own minions, punishing them for failure and is intolerant of tardiness, and will put his own safety and needs above them. Despite his ruthless nature, Ludo is weak and cowardly, having his minions do the fighting for him and quickly retreating after his army is defeated. However, he possesses tenacity, refusing to give up on obtaining the magic wand even after countless defeats.
Although Ludo is evil, he is shown to have a childish and naive side, presumably due to his upbringing which fueled his ambition for power. According to himself, Ludo's family was distant and lacked parental guidance growing up, resulting in Ludo becoming self-serving but also left him childlike and feeling bereft. As a result, when left without a proper guide, plan or in a conundrum, Ludo can quickly affix to someone else given they provide him with results and have the patience and respect to deal with him; this was evident when Ludo became attached to Glossaryck due to the strong patience Glossaryck put up with Ludo. However, Ludo can also be easily manipulated by more evil entities into doing their work under the guise of them supporting Ludo.
After he was stranded in the wilderness, Ludo developed greater determination, strength and cunning in his competition against the wildlife for food, to the point of gaining authority over the more aggressive animals. He soon loses his former cowardice, as he gains more minions over time with the power of his new wand and confronted Star with greater success compared to his previous encounters.
Ludo is a short, dull green bird-like monster with yellow eyes, a dark beak with teeth in it, and a large round head with warts on it. Unlike the rest of his family, Ludo lacks wings, or at least feathers, on his arms. When he was first introduced, he wore a green cloak with a dark fur collar and skulls, a creature's skull on his head, and flip-flops on his feet. During the events of "Ludo in the Wild", Ludo's appearance changed drastically: he no longer wears his skull cap and now has a long gray beard braided into three tails while wearing a corn chip bag over his body.
- Ludo is the fourth Disney character voiced by Alan Tudyk. The first three are King Candy from Wreck-It Ralph, the Duke of Weselton from Frozen, and Alistair Krei from Big Hero 6.
- Tudyk also provides the voice of River Butterfly in the series.
- Ludo resembles a Kappa, an aquatic yokai from Japanese mythology which is often said to resemble a turtle with a beaked mouth full of sharp teeth and a water bowl on its head. In the episode "Quest Buy", a water bowl-like patch can be seen briefly on his head.
- (March 7, 2017) Star and Marco's Guide to Mastering Every Dimension. Disney Press. ISBN 1-4847-7419-9.