Nero was a Romulan miner and captain of the mining vessel Narada. Following the destruction of Romulus in 2387, Nero sought vengeance against those he felt were responsible, ultimately resulting in his being transported back in time to 2233.
Nero's actions in the past resulted in the creation of an alternate reality. In this reality, Nero was responsible for the destruction of the USS Kelvin as well as the deaths of its senior officer, Captain Richard Robau. George Kirk's kamikaze strike against Nero's ship, as a result of Nero's kill-or-be-killed dilemma, altered the upbringing of his son, James T. Kirk, who in this timeline did not join Starfleet until 2255.
Nero was later responsible for the destruction of the alternate reality's Vulcan, which resulted in the deaths of Amanda Grayson and the majority of the Vulcan race. Nero also attempted to destroy this timeline's Earth, but his plot was foiled by Jim Kirk and the crew of the USS Enterprise.