Grant West, also known as Rapier, is "Wolf" West's second son.
As he grew up, Wolf saw Grant's potential as a soldier, due to his loyalty and obedience. However, Grant grew up hating his half-brother Jack West Jr, as he believed that Wolf saw him only as his second son, and that if he killed Jack he would become the better son in their father's eyes.
Likely as part of his father's wishes, Grant joined the U.S. armed forces upon turning 18, and soon became a Delta operator, gaining his call-sign Rapier. At some stage, Rapier was eventually seconded to the CIEF under his father's command.
After the Tartarus event in 2006, Rapier was a part of Wolf's rogue CIEF forces as they made arrangements with a few foreign nations to restore a Machine built by a race of super-ancient beings and claim the rewards of the Machine's six Pillars. Once the Saudi spy Vulture located the Firestone at Jack's farm in Australia, Rapier was assigned to accompany the Chinese forces led by Black Dragon to invade and acquire the Firestone.
Rapier parachuted down onto the farmland with Black Dragon inside an APC, and remained silent as the Chinese Major gave orders as his men pursued Jack and his friends. Once they escaped, Rapier and Black Dragon waited for Wolf to arrive at the farmhouse. After Black Dragon passed on Wolf's orders for Mao Gongli to go ahead with the torture of Max Epper, Wolf demanded that Black Dragon kill himself for his failure; when the Chinese Major objected, Wolf had Rapier kill him. When that was done, Rapier went to execute his father's orders to have their resources focused on locating Jack's plane.
A cold and compassion-less person to the point of being considered a sociopath, Rapier is the ideal soldier in his father's mind. Despite the apparently endless pride Wolf seems to feel for him, Rapier believes that his loyalty and obedience means nothing to his father so long as his older half-brother Jack is alive, and that Jack has a certain respect from Wolf that Rapier thinks he does not have. It is this belief that makes Rapier burn inside and obsess over seeing Jack die by any means necessary.