Mousewhisker is a gray and white tom.
Mousewhisker is the son of Daisy and Smoky, the brother of Berrynose and Hazeltail, and the half-brother of Rosekit and Toadkit. He was first introduced as a kit named Mouse in Twilight, when his mother Daisy took him and his littermates away from the horseplace where they were born so the Twolegs there would not take them away. After a ThunderClan patrol found them, they joined ThunderClan and Mouse was given the Clan name of Mousekit. In Sunset, Spottedleaf visits the nursery and shows him and Hazelkit a butterfly, which she says they can hunt, leading Leafpool to discover the truth about the RiverClan medicine cat, Mothwing.
He is later an apprentice, Mousepaw, in The Sight, mentored by Spiderleg, and becomes a warrior, Mousewhisker, in Outcast. In the battle in Eclipse he wounds his eye so Hollypaw guides him into battle. He is the mentor of Bumblestripe, and also Cherrypaw.
In The Forgotten Warrior, he and his new apprentice Cherrypaw eat bad prey, and get seriously ill. They are very close to death, until Cinderheart remembers her former medicine cat life as Cinderpelt, and saves the two when Jayfeather could not.