Excellinor is Alvin the Treacherous's mother, daughter of an unknown Roman, and wife to Algarick Ogglebert, and first appeared in How to Break a Dragon's Heart and has been in every book since. Her first appearance occurs when Alvin tricks Hiccup in How to Break a Dragon's Heart, Hiccup thinks he is being led to Camicazi's prison, but he is actually led to Alvin's mother's prison (A tree prison on Berserk), and left inside. Alvin's mother is a witch, displaying knowledge of plants and poisons, anatomy, and fortunetelling.
When Hiccup escapes from the prison, he forgets to lock the door properly, allowing Alvin's mother the perfect escape. Later, Alvin's mother is falling off a bridge, and tells Alvin to get the sword. Alvin, thinking she means the Stormblade, tells her he has it, but she says no, the other one. She meant Endeavour, the sword Hiccup was using. They both fall.
She later appears in How to Steal a Dragon's Sword, as Flashburn's fortune teller. She had imprisoned Flashburn and sent him looking for the Dragon Crown, but she was captured by UG. Flashburn spent twenty year searching. When Hiccup and the other tribes arrived, she lied about a dragon riot taking place at the palace. She made a prophecy about the King of the Wilderwest. She began to sabotage everyone before the Royal Swordfighting competition, and kidnapped Stoick. She sent Hiccup and his friends to search for the Dragon Crown with Flashburn, threatening to kill them with the deadliest poison in the world.
When they recovered the Crown she infected Hiccup with the poison, but Hiccup was immune, because it was a Venomous Vorpent's, and Hiccup was cured of the venom before. Hiccup releases Stoick and UG from a cabinet, and they lock her in the cabinet. When Hiccup defeats Alvin at the competition, she tricks Snotlout to throw a rock at Hiccup, causing his helmet to fall off, revealing the Slavemark, banishing him. When Furious attacks and Hiccup escapes with the very important secret compartment letter, everyone escapes with him.
Excellinor tries showing Alvin the sword's prophecy clues to the Dragon Jewel, before realizing that Hiccup stole it. She is last seen cursing his name.
One year later, Excellinor and Alvin had made slaves of many Vikings in the Barbaric Archipelago, including Gobber, Baggybum, and Fishlegs. She had been using them to find the Dragon Jewel, the location she learned when Valhallarama brought her the map, in the Amber Slavelands. When she learned that Hiccup was hidden among the slaves, she threatened to kill Snotlout, despite his loyalties to her and Alvin, unless Hiccup gave himself up. Excellinor used him to find the jewel, but he and a hidden Camicazi were captured by a Deadly Shadow dragon.
When Valhallarama brought Hiccup and the Dragon Jewel to Excellinor, the witch tried to use her silver tongue to get her to hand it over to Alvin, even explaining to her that Stoick was now a slave and the young Viking, Valhallarama was destined to marry Humongously Hotshot the Hero instead. However, Valhallarama had revealed the reasons for her quests, and only sided with Alvin was because she thought he had found the King's Lost Things. But when she found out that it was her son Hiccup who actually found them, she gave the boy the jewel and took the Slavemark, renaming it the Dragonmark, taking it as a sign to have Hiccup as the King. After a battle broke out, Excellinor, Alvin, and their followers retreated.
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When Hiccup was crowned the new King of the Wilderwest, Excellinor and Alvin were dismayed, and planned to kill Hiccup to continue the war against the dragons. After Alvin was killed by the dragon Guardians of Tomorrow, Excellinor attempted to murder Hiccup with a poisoned Stormblade. Before she could, Furious took the sword, and he flicked Excellinor away with his claw. Excellinor eventually fell down to her death, into the seemingly endless blowhole of Woden's Throat.
- Excellinor is well versed in the Barbaric Archipelago's history.
- Despite being for the elimination of the dragons, she still uses them for surveillance.
- Although she is cruel to others, she sort of has a soft spot for Alvin, being his mother.
- In How to Betray a Dragon's Hero, Excellinor accidentally bites one of her own deadly fingernails, which had previously been dipped in Vorpent Poison.