Galdor was the Lord of the House of the Tree. He was a great warrior and second only to Turgon in valour. The house of the tree was a numerous house, and with the House of the Hammer of Wrath the first to confront the enemy in the battle of Gondolin. In the wrath of their onset they caused the Orcs to "fall like leaves."
Galdor saved the lives of Tuor and Ecthelion during the battle of Gondolin. Tuor, bearing the wounded Ecthelion, came to the Square of the Well. Here were Galdor and his elves defending the place and as Tuor came he stumbled beneath Ecthelion and fell and had it not been for the rush of Galdor coming to his aid, Tuor and Ecthelion would have been slain by the Orcs. Galdor escaped with the remaining refuges the fall of Gondolin and came to the Mouths of Sirion. He was leading the company of refugees but was attacked by an ambushing orc-party. Despite the surprise of the attack he fought off the orcs with some loss to his kin, most of which inflicted by falling rocks rather than orcs.
It was known he fought with an iron-studded club but he may also have used a sling like others in the house of the tree.
He survived the onslaught of the Sons of Fëanor and was rescued by Círdan and Gil-galad and sailed to the Isle of Balar. It might be that Galdor of the Tree is the same Galdor who was sent to Rivendell by Círdan from Lindon.