Mildew is a major antagonist of DreamWorks' Dragons. He is a major antagonist of Riders of Berk, and a supporting antagonist turned anti-hero of the second season Defenders of Berk.
Unlike most of the people of Berk, Mildew has a deep hatred for the dragons, and his goal is determined to get rid of them. In the end, he reaches a peak when Mildew actually betrays the entire island of Berk and joins forces with Alvin the Treacherous, though he was never popular among his former people.
Mildew is a consummate complainer; Gobber even said of his arrival "Here comes Mildew with the complaint of the day". It is implied that his house was built so far away from the village because of his abrasive personality. Due to his staff, he carries around, decorated with dragon teeth, and the fact that he had a pair of Zippleback feet, a Monstrous Nightmare claw, and a Gronckle head in his house, it can be inferred that he was an excellent dragon-slayer in his glory days, perhaps even a better one than Stoick the Vast, which would explain his rude attitude toward him. He raises cabbages, which he probably sells to the rest of the village.
He also seems to dislike Hiccup, probably due to Hiccup's befriending of the dragons, and seems to relish the idea of Hiccup being gone, as evidenced by his attempt to turn Hiccup over to the Outcasts.
Mildew is also frightened of certain dragons, in Dragon Flower, He was scared of the Scauldron that Hiccup and the other Vikings were trying to get some venom from, which later bit Mildew on the backside. Also in the We Are Family Part II promo, a Whispering Death snarled at Mildew, which involved Mildew running away on a Nadder.
Mildew's most defining traits are his hatred towards dragons and his affection towards his sheep Fungus. In the early seasons, he led the townspeople of Berk in protest against dragons by lying about them and even using tools to frame the dragons for destroying property, but failed in humiliating ways resulting in him getting his just desserts. Later, Mildew has been revealed to be a traitor working with the Outcasts, giving him a more dangerous role. In "We Are A Family Part II", he breaks down in tears when the Outcasts imprison him and take Fungus away to cook him. He then tries to redeem himself and listen to Hiccup, even being willing to befriend a dragon under his guidance. But when the Outcasts attack, Mildew tells Hiccup that he's sorry before his grip slips and the Outcasts recapture him, expressing remorse and telling the Vikings to leave him. But in reality, Mildew was lying about redeeming himself and he was only using Hiccup to gain information for the Outcasts, laughing evilly alongside Alvin. Afterward, he suggests to bury Whispering Death eggs to destroy Berk, which contradicts Mildew's original goal of banishing dragons for the sake of his home town, showing how hypocritical and far-fallen he has gotten.
In "How to Start a Dragon Academy", he was the most prolific of the Vikings to complain about the dragons, pushing Stoick to cage them or drive them away.
In "Viking for Hire", he taunted Hiccup over the fact that his making peace with the dragons had cost Gobber his position as Weaponsmith.
In "Animal House", he was not seen but mentioned. According to Mulch, after a storm known as "Blizzard of Orlarf," it took some Vikings a week to dig a unlucky Mildew out of the ice (and the rest of their lives, to wonder why they bothered).
In "In Dragons We Trust", Mildew frames the dragons for destroying things around Berk, successfully causing them to be banished. He then disposes of the evidence by throwing it out to sea.
In "Alvin & the Outcasts", Hiccup tries to find the evidence, but to no avail. When Alvin the Treacherous arrives and searches for the "Dragon Conqueror" (Hiccup), Mildew tries to tell him but is knocked out by Astrid. At the end of the episode, he was furious to see the dragons once more- the village having accepted them back after the dragons helped them drive off Alvin's men-, but was warned by Stoick, along with Hiccup saying that he may not have the evidence that proved he framed the dragons, but will not forget it, leaving a frustrated and disappointed Mildew.
In "Dragon Flower", Mildew was seen buying mysterious items from Trader Johann, in exchange for cabbages. The next day, all of the dragons become ill for an unknown reason. Although everyone throws out what they bought from Johann, the dragons are still sick. Fishlegs tells them that the cause is the blue oleander flower, which is poisonous to reptiles which means poisonous to dragons. Tuffnut says that he saw Mildew plant them at night. When Stoick, Hiccup and Astrid interrogate Mildew, he pretends to not know of the flower's "special properties." Hiccup, Stoick, and Gobber board a ship to find the Scauldron, a dragon that feeds off the oleander, and whose venom can be used as an anti-venom. Mildew is dragged onto the ship, much to his displeasure, because it was his fault the dragons were sick. When the Scauldron is found, Mildew is threatened by Stoick to wind up with the bucket that's supposed to be used to get the venom or Stoick will throw him overboard. However, before the venom can be drained, the sea dragon escapes, but not before biting Mildew's butt, trying to get the flower that was stuck to his pants. Gobber takes Mildew back to his workshop, and uses a large needle-like object to pull the poison out of the old man, much to his discomfort.
In "When Lightning Strikes", thunderstorms strike the metal perches recently set up, and seemingly following Toothless. Mildew accuses Toothless of causing lightning strikes due to his status as 'the unholy offspring of lightning and death' (According to the Book of Dragons), and rallies up the citizens to banish the Night Fury. When Hiccup proves to everyone that the lightning is really attracted to metal, Stoick suggests putting the iron statue of Thor, built to appease the thunder god (but failed), to place it high up in the mountain, where the gang puts it directly outside Mildew's house. When the next storm comes, the lightning goes through the statue and into Mildew's house, shocking him repeatedly.
In "We Are a Family Part I", it is revealed he set a trap for Hiccup and Toothless by forging a map to an island with Night Furies. It is also revealed he has joined the Outcasts. His method of trickery was personal and devious. He used Hiccup's love for Toothless as bait, and then lured them both into a trap. Not only this but he ensured that none of the other kids would come. His actions alone led to Hiccup and Toothless being captured by Alvin and his men. Upon seeing Hiccup captured, he openly mocks him for falling into a trap set by a silly old man. It is unknown how long Mildew has been in league with Alvin, but it might help explain how convenient Alvin's arrival to the island was in episode six.
In "We Are A Family Part II", Mildew begins to regret what he has done after Alvin takes away Fungus to be cooked. He then helps Hiccup escape, and befriends a Deadly Nadder. At the end, though, it is revealed that he and Fungus were all putting on an act: Mildew truly is a traitor to Berk. He then begins to tell Alvin the information he learned from Hiccup.
In "Live and Let Fly", Mildew came up with the idea to plant a cluster of Whispering Death eggs in a underground network of tunnels so that they would hatch and destroy Berk. He and Savage oversaw this plan being put into action while Alvin and his wild dragons distracted the dragon riders, but what he was unaware of was that one of the eggs was a Screaming Death egg.
In "Worst in Show", Mildew, Alvin and Savage infiltrated Berk to investigate what happened with their previous plan, which, unknown to them, resulted in the creation of the Screaming Death. Mildew managed to save himself from Alvin's wrath by suggesting they use the tunnels to infiltrate the Dragon Academy to kill, spy and kidnap and, later on, helped the other two to kidnap Meatlug, who had been neglected by Fishlegs at the time. When tried to make their escape, he was knocked unconscious by Butt and Head, who had been trained by Ruffnut and Tuffnut, and only came around to see that they were all drifting on wreckage. Alvin immediately knocked him unconscious when he tried to make them look on bright side.
In "A View to a Skrill Part II", Mildew then oversaw the training of the Skrill when Alvin formed an alliance with the Berserkers.
In "Cast Out Part II", he was then seen feeding a Whispering Death as he showed Hiccup where the eggs came from that were planted under Berk and asked if there was a Screaming Death egg and was later seen fighting Dagur and his Berserkers.
- During In Dragons We Trust, Mildew mentions that he had three wives, who all died at some point to which he states are pleasant memories, suggesting he did not like them despite being married to them.
- He also seems to be considered quite ugly by Viking standards, as evidenced by Gobber, claiming he was hideous, and that his bare behind was the most disturbing thing he had ever seen. And Astrid dropping him in distaste after Alvin had turned his back.