Merlin's Helm was a powerful mechanism that was created by the all-powerful Wizard, Merlin. Seven companions went on a quest to find the Helm in the Shadow Isles, including, Sir Bron of Westhold, the Doctor, Ian Chesterton, Alammar of Silverwood, Thurguld, Kilvenny Odoyle and Captain Tristram. While searching the island, they found Prydwen, Merlin's space ship and the Helm was inside.
However, after the arrival of the Human Empire, Captain Shannon wanted to take the Helm for the good of the Empire. They reached the Helm first and Ivanov wore it, but with its overwhelming power, was too weak. He died under the rubble of Prydwen.
The now six companions returned the Helm back to Fluxford where Gramling wore it in order to stop any attack from the outisde, especially from Marton Dhal. It was trick however, and Dhal managed to get his hands on the Helm. But, underestimating its power, he died under it, and the Cephiles decided to destroy the Helm because of its tremendous power. (The Sorcerer's Apprentice)