It follows the adventures of Star Butterfly, heir to the royal throne of the dimension of Mewni, who is sent to Earth so she can complete her education and learn to be a worthy princess; and Marco Diaz, a human teenager.
On her 14th birthday, she is given the family heirloom - the royal magic wand - but after she causes a big accident, she is sent to the Earth dimension as a foreign exchange student.
By the time she pitched the idea to Disney, she had made the character older, and an executive suggested she would have actual magical powers, leading to the current foreign exchange student concept.
[10][11] Star wears a sea green dress with a pink octopus on the front and magenta and orange striped leggings as well as purple boots with a rhino design.
His success results in him getting regular royalty checks of 650 dollars, the cash being used as a running gag in multiple episodes in Season 2.
As a teenager, she succeeded to the throne and leadership of the Magic High Commission when Toffee killed her mother, Comet Butterfly, during his attack on Mewni.
Moon is shown to be a resourceful and capable fighter in her own right, with powerful magical abilities, experienced horsemanship, keen senses and extensive knowledge of the geography and history of Mewni.
After eventually learning that she and Star are of Pie Folk descent and accidentally wounded by Eclipsa when forced to harm Meteora, Moon ends up in the magic dimension and loses her memories.
It is later revealed that Moon ordered Rhombulus to free Globgor and created Mina's army of Solarian warriors to take back the crown.
The Johansens are portrayed as rough, Viking-like barbarians fond of the outdoors and fighting who allied with the forces of Mewni in the war against the lizards led by Toffee.
He is shown to be physically strong and a relatively bold, inspiring military leader, but was a poor administrator when left in charge of Mewni in Moon's absence.
He casually mocked Marco as the "safe kid" and unhesitantly accepted Queen and King Butterfly's bribe to let Star attend the school.
They include Beard Deer, Bearicorn, Big Chicken, Boo Fly, Lobster Claws, Man Arm, Spike Balls, and Three-Eyed Potato Baby.
Jeremy Birnbaum (voiced by Joshua Rush) is a bratty spoiled kid and Marco's rival whose parents sponsor Sensei's dojo.
Brittney Wong (voiced by Minae Noji) is a spoiled rich student and head cheerleader of Chinese descent who would often be annoyed by Star's antics.
While he initially died after Ludo burned the book in "Battle of Mewni", Glossaryck was resurrected in "Rest in Pudding" but appeared to have his intelligence regressed that of a household pet, being only able to say "Globgor!
Thomas Draconius "Tom" Lucitor[GB] (voiced by Rider Strong) is the hot-headed three-eyed demon crown prince of the Underworld, being part Mewman on his father's side.
Three centuries before the events of the series, Eclipsa was imprisoned in crystal for the use of "dark magic" and eloping with Globgor, a monster; while her child, Meteora, was replaced with a Pie Folk girl named Festivia, who is the true ancestor of Star's bloodline.
When the kingdom was attacked by Toffee, Moon made a deal with Eclipsa to learn a forbidden spell capable of killing him in exchange for her freedom.
[22] When the trial occurs in "Butterfly Trap", Eclipsa helped Star and Moon in forcing the Magic High Commission to admit their actions against her.
During Season 4, setting her palace in the restored Monster Temple, Eclipsa made several attempts to free Globgor from his crystal prison while also trying to win the respect of the Mewmen.
Throughout Season 3, Glossaryck constantly mentioned his name, trying to warn everyone before coming to the point after Meteora was turned into a baby and Eclipsa reunited with his crystallized body at the Monster Temple.
After imagining them saying loving, supportive things for a while, the caricatures revert to memory and he compulsively puppets the abusive, denigrating personalities his parents actually have.
Ludo Avarius (voiced by Alan Tudyk)[3] is a major avarian from Mewni with a round head and a beak and wears a cap made out of the upper part of a creature's skull.
By end of the episode, Dennis learns to stand up to his parents and Ludo decides to remain in the void, stating that he still has a lot of issues to work out.
In the Season 4 episode "Princess Quasar Caterpillar and the Magic Bell", after to falling back to his old ways, which he curses himself for, Dennis shows up and reveals he bought the deed to Castle Avarius and hired all of Ludo's old minions to rebuild it.
Toffee (voiced by Michael C. Hall[24]) was a Septarian, a race of humanoid lizards with regenerative abilities that make them essentially immortal,[25] who had been an enemy to Star's family.
Raised by robot headmistress Olga as Miss Heinous, Meteora forgets her identity while eventually taking over as the headmistress of St. Olga's Reform School for Wayward Princesses, with the support of her robot assistant Gemini (voiced by Bennett) and the Septarian bounty hunter Rasticore Chaosus Disastervaine (voiced by Chris Tergliafera).
Mina eventually betrays Moon once realizing she intends to allow Eclipsa and her family to leave in peace, resolving to exterminate them and all monster sympathizers.
Mina survives the destruction of magic and is offered help by Moon which she rejected, she became powerless yet still adamant of her idea to commit genocide on the monsters of Mewni while running off into the woods.