Grant West, also known as Rapier, is "Wolf" West's second son and Jack's half-brother.
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.
Rapier joined his father in relocating to Diego Garcia, where the CIEF spent the next two months researching the locations of the remaining Vertices. After Felix Bonaventura discovered in unison with Yanis's intel the existence of a Fabergé Egg containing images of the Vertex entrances and was kept in Genghis Khan's lost arsenal somewhere in Mongolia, Rapier went along with his father's team to claim it.
Along with one of Mao's units, Wolf, Rapier and Bonaventura discovered the arsenal beneath a concealed meteor crater, and made their way inside to claim the Egg. As they entered the arsenal vault, Rapier noted several bodies, and Wolf corrected his assumption that they were sacrificial victims but rather the slaves who had built the arsenal. Rapier managed to snap a few images of the Egg with a basic camera before they were ambushed by Tank and the Brotherhood, who destroyed the Egg. When Jack and Wizard appeared, Rapier was astonished and furious to learn that his half-brother was not dead. When Wolf took down Tank, Rapier revealed he had salvaged the mission by taking the photos he had, and fired upon Jack and the fatally wounded Wizard before departing the arsenal.
A few days before the due-time to lay the third Pillar, Rapier joined Wolf's invasion on the Hokkaido Vertex, carrying the Philosopher's Stone in his pack as he landed on the tsunami-receded shore. However, the heavy resistance the Japanese put up resulted in Rapier getting pinned down. Knowing that without the cleansing stone they could not succeed, Wolf ordered his men to get his son into the Vertex, but it was Jack, Lily and Zoe was got Rapier to safety, albeit with Jack taking Rapier's pack with the Sacred Stone in it. Though Rapier wanted to kill Jack and the others at first opportunity, Lily revealed she knew how to traverse the trap system, and so Wolf proposed a temporary alliance to lay the Pillar, which Jack reluctantly accepted.
During their journey through the Vertex, they came across the trap containing the Vertex's Pillar, and were forced to wait until they could get access. During their time waiting, Rapier took a moment while Wolf slept to threaten Jack, telling his half-brother that he would kill him to earn the respect he believed Jack still had from Wolf, and backed down when Zoe ordered Rapier to get away from Jack. Rapier was selected to be a part of the team to try and claim the Pillar from the trap, but was way-laid by gunfire from the Japanese and forcing Jack to get it instead.
When they finally made it to the inverted pyramid, Rapier helped Astro and Zoe secure the winches Wolf and Jack used to secure their boats as they headed out to lay the Pillar, and more resistance from the Japanese caused Rapier to lose his grip, but ultimately the Pillar was set. As soon as his father and half-brother were back on the dock, Rapier aimed his gun at Jack, believing he and his people were of no further use. Wolf, however, ordered Rapier to stand down, and though furious he reluctantly followed his order. As they prepared to leave with the Pillar, Rapier set off a grenade to collapse the bridge in an attempt to strand Jack and the others within the Vertex. Once Wolf, Rapier and Yanis exited the Vertex, however, they were captured Russian forces.
Taken to a dam in Russia, Rapier and several other players in the Machine-restoration mission were confronted by the Russian royal known as Carnivore, who revealed his intention to take the Pillars and their rewards, and to manipulate everyone else into completing the Machine's restoration for him. Though Carnivore was unwilling to risk both Jack Wests being loose, he offered the chance for one of them to continue the mission on his behalf, depending on whether Jack or Rapier won a fight to the death, with Rapier to remain a hostage to ensure Wolf's cooperation if he won. Relishing the opportunity to finally kill Jack and earn his father's respect, Rapier quickly agreed.
Taking to the dam's catching tray, Rapier squared off against Jack in spite of the cacophonous noise and rushing water, managing to get some good hits in despite Jack's attempts to remain wary of the fighting style he had seen Rapier use in the third Vertex. As they ended up clinging to the steel struts of the cage, Rapier continued to fight hard and comment on how he was the worthy son, but Jack was able to open a gate in the tray and send it swinging into Rapier's face. The force of the blow hitting him either stunned or killed Rapier; even so, his grip released and sent his body into the turbine below where he was churned into nothing.
Wolf was stunned when he saw Jack return instead of Rapier, with Carnivore admitting he had though the brawnier Rapier would have won; in any case, his failure to kill Jack resulted in Wolf being imprisoned by Carnivore's men in a tank of formaldehyde.
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.