He is voiced by T.J. Miller for first, second films, TV shows and later Justin Rupple for The Hidden World.
Although never said throughout the show, Tuffnut seems to be slightly more dominant twin than his sister and has a more prominent role, especially in the TV Series. Together, he and his sister love to get into trouble, even if it means getting scolded by the chief of the village. Tuff likes the idea of Ruff being in danger (as he stated that when Ruff was on fire one time, he just watched for a while before he decided to save her). Tuff enjoys the chance to argue and wrestle with his sister, although it usually ends with Ruff overpowering him, either verbally or physically. He shares many similar traits with his sister. The only thing that seems to be apparent in difference, is he enjoys gross things as opposed to his sister (as seen in Gift of the Night Fury). Despite having a close sibling relationship, Tuff is frustrated when he has to share everything with his sister, but he's willing to make amends with Ruff to save his dragon. Although sharing rivalry with his sister, on occasion, he will save her if she is in trouble. He often thinks highly of his own skills, claiming that he was the world's deadliest weapon. In the TV series, Tuff appears to show a thrill-seeking and masochistic personality, displaying an attraction to dangerous situations and seems to enjoy or looks forward too whatever bodily harm he recieves (usually by his sister).
How to Train Your Dragon
Joining the same Dragon Training class as Hiccup, at first Tuff delights in taunting Hiccup over his poor performance although he doesn't have much success either due to the fact that he couldn't get along with his sister in battle. Later, however, when Hiccup displays an amazing talent for subduing the Dragons, he becomes his avid fan (often pushing and shoving Ruff to be the first to talk to him). The twins decide to help Hiccup fight the Red Death and bond with the Zippleback that had been trapped in the training arena before.
To confront the Red Death, the twins mount a Hideous Zippleback, which fits their fractious relationship, the two naming the dragon Barf and Belch. Each head seems to agree with one of the twins in particular - Ruff taking Barf and Tuff Belch, and they ride it to great effect in the final battle and afterwards. Notably, they were the only ones not forced from their dragon in the final battle.
How to Train Your Dragon 2
In the second film, Tuff would not let his dragon be taken by Drago Bludvist. Tuff was disgusted by his sister's attraction to the Dragon trapper Eret. Following Stoick's death, Tuff rode one of the baby scuttleclaws despite difficulty in riding them back to Berk.
How to Train Your Dragon: The Hidden World