Mildew

Berk's local curmudgeon and cabbage farmer introduced in Riders of Berk. He opposes dragons being a part of Berk and does and says anything to make his wants and need known. He also has a sheep named Fungus, that he frequently carried around everywhere.

Mildew seems to enjoy stirring up trouble around Berk and is the "nasty word of mouth" around the village. It's hinted that Stoick personally decided that Mildew's house would be placed as far away from the village as possible which is why he lives behind the Great Hall. Stoick and Mildew never seem to be on too good of terms, and Gobber spends most of his conversations with Mildew insulting him.

In terms of Berk's new addition of dragons, he's completely opposed to them and still carries all the old violent and hatred towards them. In How to Start a Dragon Academy Mildew is responsible for stirring up the town to want the dragons to be caged, and eventually makes it so Stoick has no choice but to ask Hiccup to send them away. Even though his plan didn't work, he's still seen in Viking for Hire to fuel Hiccup's guilt towards ending Gobber's livelihood in making weaponry. 

Mildew's scheme against the dragons return in In Dragons We Trust when Mildew concocts a perfect series of misfortunes on Berk--stealing boots, vandalizing the Great Hall, and burning down the island's armory--and blames them all on the dragons. Mildew made boots that were modeled after a Zippleback's feet to make dragon footprints in the suspected areas as well as made a fake claw that he used to deface the Great Hall. Although this evidence is seen by Hiccup, Mildew threw the boots and claw into the ocean before Hiccup got a chance to prove his findings correct.

As of Alvin and the Outcasts, Mildew is off the hook due to there being no evidence towards him committing the crimes, but with the dragons back on Berk, it's assumed he'll try to get rid of them again. In the same episode, it's revealed that Mildew really does have something against Hiccup personally, and was willing to turn Hiccup into Alvin if Astrid had not knocked him out by punching him.

Also revealed in In Dragons We Trust Mildew has been married three times, and each of his wives--to Mildew's happiness--have all died. He does, though, keep pictures of his ex-wives painted on shields and hung on his wall...alongside a picture of Fungus. But he puts them up there more to mock them then to remember them lovingly. It's believed that he perhaps killed his wives since he's so happy about all three of them being ironically dead.

Later in Dragon Flower Mildew has yet another plot against the dragons, but this time he's plants deadly flowers in the village square that are poisonous to dragons, thus making them sick. Though he still cannot be pinned for his crimes for there's no evidence towards his true intentions.

In When Lightning Strikes Mildew capitalizes on the frequent and mysterious lightning storms and get the village to believe that the Thor is angry at Berk for housing a night fury which is the "unholy offspring of lightning and death itself". His logic is legit for the time period and believes of Vikings, but takes no small motions in trying to get Toothless thrown off the island as a sacrifice to pay tribute to Thor and ask for his forgiveness.

Once Hiccup proves that it's not Toothless that's attracting the lightning, but the metal perches and statue that they recently put up, Mildew's theory is once again, discredited, and as an unofficial punishment Snotlout put the metal Thor statue in front of Mildew's house, which attracted the lightning straight to him in every event of a thunder storm.

Mildew's crimes still continue, in a shocking revelation, in We are Family, part 1 in which it's revealed that he's been working for Alvin for quite some time. He and Alvin's latest scheme included forging notes from Bork into his private archives that revealed a secret island filled with Night Furies. Hiccup and Toothless willingly went there only to get captured. Mildew's house was cleared out as of that episode, so it's assumed that he wasn't planning on going back to Berk.