"One of Valka's dragon rescues, Gruff was blinded by a tree snare left by a band of Drago Bludvist's trappers. Fortunately for Gruff, Valka and Cloudjumper located him during one of their dragon raids and freed the sightless Hobblegrunt, along with several other dragons. In fact, it was during this dragon "jailbreak" that Valka called upon her Bewilderbeast to destroy the trappers' fort, obliterating it in a blast of green ice and dispersing several of Drago's underlings, including Eret, Son of Eret. Despite his inability to see, Gruff still lobes a happy and productive life in the Bewilderbeast's arctic nest, thank to the large fin crowning his head. As with other Hobblegrunts, this fin allows Gruff to sense his surroundings and react to incoming threats or obstacles a split-second before sighted dragons!"
Gruff used to be an ordinary wild dragon, until he was caught in a tree snare by one of Drago's Dragon Trappers, and the incident blinded him. Fortunately, Valka and Cloudjumper had found him. Discovering who had maimed him, Valka asked the Bewilderbeast for aid and the king of dragons attack Eret, Son of Eret's fortress and destroy it. Despite being blind, he still lives a happy life in Valka's Mountain.
Valka introduced Gruff, Lump and Thump to Hiccup and Toothless, telling how each one got their injures. Although not seen, Gruff may have participated in the battle at Valka's mountain. After Drago's Bewilderbeast killed Valka's, Gruff was forced by the new alpha to go to Berk. There, Toothless managed to free Gruff and the other dragon's from the Bewilderbeast's control, which immediately started firing at the giant dragon. After Drago's defeat, Gruff stayed on Berk, along the other dragons.
Gruff is so far the only known member of the Hobblegrunts. Due to the body size, he seems not to be a matured individual. He has a big frill at the back of his neck, clawed wings, sturdy nadder like legs, and short arms. His eyes are dull-colored caused by the snare that blinded him. He has long teeth protruding from the lower mandible. He resembles a theropod dinosaur like a Speed Stinger does. He changes color based on its mood, like all Hobblegrunts, the only parts that are always the same coloration are the blue spots he has all over his body.
Gruff is apparently very sensitive and shy. This was largely due to past incidents and traumatic damages he carries. However, this sensitiveness helps others to know subtle movements in nest mates' emotions, and with his abilities native to his species, the Hobblegrunt can be very useful and helpful as part of the warning system for the Sanctuary. According to Dragons: Rise of Berk, Gruff is very intelligent and can be trained to find its way to Berk, showing that he can fit in rather well with other dragons. Gruff is also mentally strong to live happily without sight.