Grimbeard the Ghastly is a character that existed before the events of the books.
Grimbeard was married to Chinhilda and had three sons; Thugheart, Chucklehead, and Hiccup Horrendous Haddock II . Grimbeard broke Chinhilda's heart when he abandoned newborn Hiccup on a mountainside for being a runt, so she became the ghost that haunts the Bay of the Broken Heart. Hiccup the Second grew up with dragons after being rescued from starvation by them and years later Hiccup the Second returned and started the first Dragon Rebellion lead by him and his brother Furious. It was meant to be a peaceful talk but it quickly turned into a massacre when Thugheart lied to Grimbeard about Hiccup's intentions. Hiccup the Second was killed by Grimbeard, ran through with the Stormblade, but when he begged to Furious not to hurt anyone, Grimbeard realized what he'd done and tried to stem the blood but it was too late, Hiccup was dead and Grimbeard driven to bitter sorrow. In guilt, he burned down what remained of his kingdom and sailed off, never to be seen again.
But before he left, he set up a scavenger hunt for ten items which were his favorite treasures, they were later called the King's Lost Things. Whoever found the lost things and brought them to the Island of Tomorrow would become the next King of the Barbaric Archipelago. He hid the lost things behind terrible dragons, trusted people, and great puzzles. He set up the scavenger hunt, because he hoped that the next King would be a better King than he ever was.
|“||Grimbeard had won a glorious treasure through his brilliance at piracy and swordfighting, a treasure that included his famous sword, the Stormblade. But after twenty years if glorious rule, Grimbeard had disappeared on a mysterious quest, and neither he nor the treasure were ever seen again.||”|
|— Book 2|
Chucklehead and his descendants became the chiefs of the Hairy Hooligan Tribe and it is him Hiccup, Stoick, Baggybum and Snotlout are descended from. Thugheart was banished and formed the Outcast tribe and is it him that Alvin the Treacherous and Fishlegs is descended from. Hiccup, Snotlout and Fishlegs are his great-great-grandsons.
He was first mentioned in this sequel to the book How to Train Your Dragon. He was not only the world's greatest pirate, but Hiccup, Snotface Snotlout,Fishlegs, Stoick the Vast, Alvin the Treacherous and Baggybum the Beerbelly's ancestor as well. Grimbeard buried his vast treasure somewhere on the Isle of Skullions before his death, and Hiccup has to solve a riddle to find it before Alvin the Treacherous does. Hiccup finds the treasure underwater in a cavern with Alvin The Treacherous and Fishlegs but, the treasure is guarded by a Monstrous Strangulator. Grimbeard wielded a sword named Stormblade which he kept with him on all his journeys until it was lost and taken by Alvin the Treacherous who uses it to attempt to kill Hiccup.
Grimbeard is thought about a lot by Stoick the Vast. He often wonders what Grimbeard the Chief would do in a particular situation, as he is highly respected and thought of as being an ideal Viking chief. Specifically, Stoick wonders what Grimbeard would do after having received a threat from the Bog-Burglars, that Hiccup refutes as a plot of the Romans.
|“||'What kind of chief am I? he thought to himself wretchedly. Grimbeard the Ghastly would never have hesitated like this! Grimbeard the Ghastly would know it was the Bog-Burglars' fault yet again.'||”|
|— Stoick's thoughts in Book 3|
Ultimately Stoick chooses his son's explanation over what Grimbeard might have done.
Grimbeard was also mentioned again as winning the original swimming race in 3 months 5 days and 6 hours. For his prize, Grimbeard became King of the Wilderwest and asked for Murderous the Magnificent to be sacrificed to the Sky Dragons.
Wodensfang reveals Grimbeard's original name was Speedfast, and also looked very similar to Snotlout when he was young. He would not accept the Dragonmark, a sign of the Kings of the Wilderwest and Dragon-Riders, and made it the Slavemark. He then banned Dragonese after being confronted by Wodensfang. He was also the one who enslaved both dragons and humans to build the kingdom on the island of Tomorrow.
|“||Hiccup knew that Grimbeard had been the ULTIMATE in pirate-ness, the GREEDIEST, GRISLIEST, GORIEST Viking who had ever sailed and slew and farted his way across the Northern Seas.||”|
|— Book 2|
|"How to Train Your Dragon":||Absent||"How to Ride a Dragon's Storm":||Mentioned|
|"How to Be a Pirate":||Mentioned||"How to Break a Dragon's Heart":||Absent|
|"How to Speak Dragonese":||Mentioned||"How to Steal a Dragon's Sword":||Mentioned|
|"How to Cheat a Dragon's Curse":||Absent||"How to Seize a Dragon's Jewel":||Absent|
|"How to Twist a Dragon's Tale":||Absent||"How to Betray a Dragon's Hero":||Mentioned|
|"A Hero's Guide to Deadly Dragons":||Absent||"How to Fight a Dragon's Fury":||Absent|
Unknown (Possibly Grimbeard's father)
|King of the Wilderwest
Hiccup Horrendous Haddock III