Forrest's father, Lord Brandon Umber, had been charged by Lord Edmure Stark with the task of rebuilding Moat Cailin before the beginning of the first era. The North feared invasion, and wanted to rebuild the ancient fortress. After Brandon's death the task fell to Forrest. It was completed before the end of the first era.
Upon his arrival at the capital Forrest raced to the Throne Room as Loren Lannister, Hand of the King, held court. In the confusion following the sack the lord was not confronted while entering the city. His attempt to assassinate Loren was stopped by members of the Kingsguard, but Forrest managed to kill three of the white cloaks before being slain by ser Thaddius Lannister.