Alvin the Treacherous is a Viking, leader of the Outcast Tribe that has appeared in the series Riders of Berk and in the books, being Hiccups arch enemy. 

Banished from Berk long ago, he's known to live on a far away island, Outcast Island, and plans to get revenge on Berk, also wanting Hiccup to teach to his minions to ride dragons. This plan was born after his first series' appereance. Some dragons attacked and outnumbered the Island's habitants and Alvin travelled to Berk to find the Dragon Conqueor. Hiccup revealed hiself to be the one since the Outcasts were holding the Vikings' hostages and was brought to their island. Tricking Alvin, Hiccup was able to ride Toothless and, later on, was helped by his friends on their dragons and by Berk's vikings, arrived by boat. Stoick is able to tie Alvin's hands on a boat set on the water and then burned by the dragons. The Outcast leader however is able to escape and decides that, since Berk's vikings are able to fly on dragons, his Outcasts should do too.

To do so, he hold hostage Heather's parents and forces her to become his spy. She was able to bring him the Book of Dragons but, thanks to a plan made by Astrid, the book is recovered and brought back safe to Berk. Alvin, after some failed attempts while having the books, understands that is not the book they need but Hiccup. With a trap, the Outcasts are able to get him when Alvin was trying to train a Nadder without results but the arrival of Snotlout and Toothless ruin his plans and Alvin is, once again, defeated, angering him even more.

He is able to smbush and capture Hiccup and Toothless while the two lands on an island where Toothless' family should live. Alvin wants to finally learn to tame and train dragons to claim Berk for himself. This plan is set with Mildew, revealing him as a traitor of the vikings. Back in the Outcast Island, Hiccup suggests some helpful tips for the dragon's cages and Alvin immediatly applies the changes. Mildew is arrested and imprisoned with Hiccup but this is also part of the plan, as Mildew is supposed to put a temporary truce between him and the boy, in order to gain some of Hiccup's secrets. The plans succeeds and Alvin is seen using a captured and tamed Whispering Death, finally reaching his goal.

In the last episode of the series, Alvin and his Outcasts are seen to attack Berk but this is just a diversion to let Mildew place Whispering Death's eggs under the island of Berk.

While in the series, Alvin is supposed to own a Whispering Death but in the books he doesn't have one although he rode some.