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 despite having never met him and Jack being unaware of Grant's very existence, 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.
When the coalition of minnows rendezvoused at Mortimer Island to make use of the Sacred Stones and Pillars they had obtained thus far, Rapier stood by his father's side as they watched the proceedings via the base's security feed.
After some members of the coalition team were captured following the placing of the first Pillar at Abu Simbel, Rapier accompanied Wolf to the Lalibela mine, watching silently as his half-brother was crucified onto a stone slab. Rapier remained silent as their father spoke to Jack, and upon introducing Jack to Rapier, the younger brother remained impassive despite Wolf's commendation of his skills compared to Jack. After watching another slab be dropped on top of Jack, Rapier inquired as to what they were going to do about Stretch, with Wolf informing him that they would claim the bounty that Mordechai Muniz had set on him.
Over the next few days, Rapier took part in the CIEF's search for Epper's group and the Neetha tribe, and upon locating the Neetha village Rapier took part in the assault. During the attack, Rapier led a team into the sanctum above the maze, finding the Philosopher's Stone, first Pillar and Firestone.
Rapier went with Wolf's CIEF team to the second Vertex beneath Table Mountain, with Yanis guiding their way through the trap system. Rapier watched in shock as Switchblade killed Broadsword, revealing himself as a member of the Japanese Blood Brotherhood, and prepared to drop the Pillar into the abyss and doom the world to the Dark Sun. Though Rapier was unable to do anything, Jack, who was still alive, managed to get to the inverted pyramid's tip, tousled with the treacherous Switchblade and place the Pillar before the Blood Brotherhood member dropped them both into the abyss. Though they were surprised to have seen Jack alive, Wolf sent Rapier to claim the Pillar from the pyramid's peak, and once he'd done so, Rapier and the rest of the CIEF departed the Vertex.
After leaving the Second Vertex with the Pillar, Rapier and his father met up with Mao, Iolanthe, Vulture and Scimitar, wherein the group began discussing their next move for the placing of the remaining Pillars and locating the vertices in the three-month interim before the third Pillar's placing.
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 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.