|“||“If anybody gets over the wall first, I’ll make sure you get the Mural Crown. Victory for the Fifth!”||”|
Not much is known about her past, except that she started her journey to Camp Jupiter at the Wolf House. After arriving, she joined the Roman Legion for a full ten years of service (as of The Son of Neptune), eventually becoming the senior Centurion of the Fifth Cohort.
Jason Grace begins to remember that they once were friends.
Gwendolyn makes her first appearance when Frank and Hazel invite Percy to join the Fifth Cohort. Gwen and Dakota give each other pained looks, as if to say "Here we go again." She seems to be close friends with Dakota and is an active member of the Senate of Camp Jupiter.
During the Roman War Games, Gwendolyn and Dakota lead their cohort around the city and toward the Field of Mars. Gwen then headed to the officer's meeting to form a strategy for the games, as the Third, Fourth, and Fifth Cohort were on the offensive against the First and Second Cohort, who were defending. Despite the grim news that they were being sent in first to soften the defenses, Gwen tried to lift their spirits by saying that maybe they would have good luck this time. She then proceeds to give everyone their orders, sending the first line with Dakota in tortoise formation (testudo), telling the second line to use ladders and take care of the elephant, and telling Percy, Frank, and Hazel to do whatever. She then promises that the first person over the wall would be awarded the Mural Crown.
After Frank, Percy, and Hazel manage to take out the defending base's defenses, he calls to the Fifth to attack. Gwen quickly gets over her shock and relays the order to the rest of the cohort, who quickly rush to attack with Hannibal. Once the Fifth manages to overtake the base, a camper is seen yelling for help because Gwen had been stabbed from behind by a pilum. The medical team tried their best, using gauze and powdered unicorn horn to stop the bleeding. They even tried to feed her nectar, but eventually one of the medics told Reyna that she had died. Hannibal nuzzled her hair as she laid on the ground, while Reyna announced that there would be an investigation on who killed her. It was then that Frank noticed that the pilum belonged to the First Cohort, and Octavian currently didn't have one.
However, before Frank could do anything, Gwen let out a gasp as she returned to life. Despite having a seven foot long spear in her chest, she didn't seem to notice and asked what everyone was looking at. She explains that she was at the River Styx and Charon had asked her for payment to cross, but she found an exit door and used it to leave the Underworld. Frank then tells Gwen to close her eyes, before asking Percy and Hazel to help pull the pilum from her chest. The instant it was removed, Gwen's wound instantly healed up and she didn't even feel the pain from it. Hazel then explained to Gwen that she had died, much to her surprise.
A moment later, the god Mars appeared to issue a quest, with the permission of Jupiter. He explains that the god of death, Thanatos, isn't guarding the Doors of Death. He then points to Gwen explaining that she should be dead but isn't, as well as the fact that monsters aren't returning to Tartarus anymore, and dead mortals are returning to the land of the living. Eventually, demigods like Centurion Shishkebab (Gwendolyn) will be able to find exits to the Underworld easily, and eventually humans will as well. Because of this, he gives a quest to his son, Frank, to go to Alaska to find and free Thanatos.
The next day, Gwen and Nico are seen talking before being let into the Senate by Terminus. Reyna announces that after ten years of service, Gwendolyn had decided to step down to attend college, while Frank would replace her as the cohort's centurion (much to the Senate's dismay). She gives everyone a brave smile, but Percy notes that she looks tired, most likely from the previous nights events.
Gwen is mentioned later, as after Camp Jupiter manages to defeat the Giant Army, Thanatos had not taken her back to the Underworld, even though she had died before. She also appears at the Senate meeting. When Percy tries to convince everyone that the Prophecy of Seven is beginning, Gwen backs him up. She praises his abilities on the battlefield, restoring the honor of the Legion, and even calls him a hero of Rome, even if he is a Greek demigod. She then goes to watch as the Argo II prepares to land at Camp Jupiter.
Gwen is described as "optimistic" by Frank Zhang, being the main reason that the Fifth Cohort remained positive through all their hard times. Even when given bad news (like the Fifth Cohort being sent into battle first), she tries to lift her cohort's spirits, even if it doesn't always work.
In Welsh, Gwen means "fair bow" or "blessed ring."
- It is hinted that she was killed by Octavian, but came back to life due to Thanatos being chained and the Doors of Death being unguarded.
- She stepped back as centurion and went to New Rome to attend college.
- Gwen is nicknamed Centurion Shish-kebab by Mars because she was speared through the chest during a game similar to Capture the Flag. In The Lightning Thief, Percy claims that if his breast plate hadn't protected him, he would have been a shish-kebab as Clarisse (daughter of Ares, Mars' Greek form) had attacked him with her spear during a game of Capture the Flag.
- Despite Gwen being a Roman demigod or legacy, her name is Greek.