The region of Ladros seems originally to have been a fief of Finrod Felagund (at least, his brothers Angrod and Aegnor held "the northern slopes of Dorthonion", according to Quenta Silmarillion, "Of Beleriand and its Realms"). Finrod later assigned this land to Boromir of the House of Bëor, whose members had long been loyal in his service.
Of the House of Bëor, there were three lords of Ladros — Boromir himself, his son Bregor, and Bregor's son Bregolas. In Bregolas' time, Morgoth overwhelmed Dorthonion and Ladros in the Dagor Bragollach, in which Bregolas himself was slain. His brother Barahir and twelve faithful men, including his son Beren, became outlaws in their own land, assaulting Morgoth's forces from their hidden lair at Tarn Aeluin on Ladros' southern borders. They were betrayed by Gorlim the Unhappy,(who was himself deceived by Sauron into divulging the Outlaws' whereabouts.) and all were slain but Beren, who escaped into the south. After this time, Ladros fell under the yoke of Morgoth until it was swallowed by the Great Sea at the end of the First Age.