Kroova Wavedog was a rebellious, orphaned, and intelligent sea otter who befriended Sagaxus and Bescarum Whippscutt and brought them along on a voyage in his stolen vermin vessel, the Stopdog.
The voyage originally began with just the three of them enjoying their youth and discovering themselves, but after battling a shark and meeting the Migooch Tribe, they became embroiled with the Riftgard conflict between Triss, Shogg, and their pursuers, Plugg Firetail's freebooters and Princess Kurda. Kroova was a valued member of the party and was instrumental in the Redwallers defeat of the vermin.
Kroova played a big part in freeing the slaves at Riftgard and defeating King Agarnu. He chose to stay instead of returning to Redwall with Triss. He eventually married a pretty ottermaid, Sleeve, whom he freed. He also became the adopted father of Freedom, an unclaimed mousebabe.