newhisker/Onestar is a small, lean, mottled light brown WindClan tom with amber eyes.

In the New Prophecy, he is first seen in Midnight in a patrol. He, Crowpaw, and Mudclaw are crossing the ThunderClan border. A ThunderClan patrol made up of Brambleclaw, Dustpelt, and Squirrelpaw find them. Mudclaw tells Dustpelt that they're not stealing prey. Squirrelpaw turns to Crowpaw and asks what he has. Onewhisker, who is embarrassed to be found on another Clan's territory, and also one of Firestar's good friends, tells Squirrelpaw that it isn't a ThunderClan vole, because it ran across the border with RiverClan. Brambleclaw informs him that he was then stealing prey from RiverClan. Crowpaw tries to start a fight, but Onewhisker drags him off, scolding him. He tells the ThunderClan patrol that there is no prey on the moor and that the kits and elders are hungry. Mudclaw and Onewhisker apologize and the WindClan patrol goes away.

In Dawn, Onewhisker and a WindClan patrol venture deep into ThunderClan territory to beg for help. They are all incredibly thin. Soon, Tawnypelt of ShadowClan comes to ask for help stopping Twolegs from invading their camp. Onewhisker is seen warning Tallstar that the leader only has one life left, and that he should stay in ThunderClan camp. Tallstar refuses, and says that his duty is to the forest.

While the three other Clans reach ShadowClan, the Twolegs are almost there, and no one can find Tallpoppy and her three kits. Onewhisker finds them and races over to grab the kits. A tree topples over, almost crushing Onewhisker, but Firestar rams him out of the way and loses a life saving him. The leader lost a life for his friend, and Onewhisker thanks him and gives the kits back to Tallpoppy.

In Starlight, Onewhisker is first seen in the marshland where the Clans are sheltering. All the leaders of the Clans gather together to assign tasks. Onewhisker is angry at how Mudclaw, the deputy, acts as if he were leader. He protests, saying that Tallstar is still the leader of WindClan, and Mudclaw coldly tells him that Tallstar won't be leader for much longer. Firestar cuts into the fight, telling Onewhisker that he knows he's worrying about the aged, feeble leader, but Mudclaw is doing his duty. Onestar is still angry, but sits down.

When Tallstar is dying, he asks for Onewhisker. The warrior runs in and Tallstar tells him that Mudclaw is a good warrior, but not the right cat to lead WindClan. He then appoints Onewhisker as deputy, but doesn't use the correct words. Onewhisker is horrified and tells Tallstar no. Tallstar convinces him and Onewhisker promises to do his best. Tallstar then dies, and Onewhisker protests, saying that the old leader wasn't thinking clearly, but Firestar firmly tells Onewhisker that this is what Tallstar wanted. Onewhisker wonders what he will say to Mudclaw, and Firestar tells him that he will tell the Clans if Onewhisker wants him to. Onewhisker thanks him.

When the cats gather, Firestar and Onewhisker sit beside one another on the roots of the tree stump. Firestar announces that Tallstar is dead and Onewhisker was appointed deputy before he died. Onewhisker asks for Mudclaw to continue being deputy and that he will need his support. Mudclaw asks who will follow Onewhisker, and Crowfeather says he will. He meets Onewhisker's eyes, and greets him as the new leader of the Clan. Cats in the crowd cheer, calling Onewhisker's new name, Onestar. Mudclaw says that he will never serve as Onewhisker's deputy. Onewhisker appoints Ashfoot, Crowfeather's mother, to be the new deputy. He then goes to sit vigil with Tallstar.

Onewhisker soon claims the territory from the horseplace to the stream for WindClan.

Later, Leafpaw, the ThunderClan medicine cat apprentice, offers Barkface some healing herbs. Barkface accepts, as some of the Clan's cats had been poisoned by tainted water Mothwing accidentally gave them. In return, Onewhisker gives ThunderClan a whole slice of WindClan territory. When Leafpaw finds the Moonpool, she reports it to WindClan. Barkface says he will go with Onewhisker after the medicine cat gathering to receive his nine lives, Onewhisker nervously says they will go later then that.

Mudclaw and Hawkfrost create a rebellion against Onewhisker, and some ShadowClan, RiverClan, and even a few WindClan warriors go with them. During the fight, a bolt of lightning strikes a tree, and Mudclaw gets crushed and killed. The cats take Mudclaw's death as a sign that Onewhisker is the true leader of WindClan. Onewhisker forgives the cats who rebelled against him.

In Twilight, Brambleclaw, Squirrelflight, Ashfur, and Rainwhisker see a WindClan patrol, and ask about Onewhisker. Whitetail corrects him by saying Onestar.

When the patrol comes back, Firestar asks if he got his leader name. Brambleclaw tells him yes.

When a fox is found in ThunderClan, Firestar leads a patrol to WindClan to warn them. Onestar confirms that his warriors tracked it and were watching it, and finishes insisting that WindClan can solve its own problems.

During a Gathering, Leopardstar reports that Leafpool helped RiverClan's medicine cat, Mothwing, and Blackstar reports that ThunderClan helped them scare off two kittypets who had killed an apprentice, Onestar jumps up and asks what sort of leaders they were, accepting help from another Clan. He says that ThunderClan should stop paying so much attention to the other Clans. Cloudtail points out that they helped when WindClan was starving, and Onestar says that was different.

When Leafpool runs away with Crowfeather, Onestar accuses ThunderClan of stealing his warrior, and lets out an angry hiss when Squirrelfight says that Leafpool loved Crowfeather.

When badgers attack ThunderClan's camp, Onestar and WindClan helps to defeat them. Onestar tells Firestar after the battle that they had helped WindClan in the past and would WindClan helped them in return.