The Story in Titanfall 2
Jack Cooper is a rifleman in the Militia. He aspires to become a Titan Pilot and is receiving off-the-books training from Captain Tai Lastimosa to prepare for his candidacy. The two are part of a Militia force which attacks the IMC-held planet of Typhon. In the initial battle, the Apex Predators, a group of mercenaries led by Kuben Blisk and contracted by the leader of the IMC's science division, General Marder, mortally wounds Lastimosa and incapacitates his Vanguard-class Titan, BT-7274. With his dying breath, Lastimosa transfers control of BT to Cooper.