Oshawott was one of the Unova Region's starter Pokemon who was under the care of Professor Juniper. When the new trainer, Trip and Ash Ketchum who had arrived from Kanto witnessed the three Pokemon being shown for the first time, Oshawott made such a good impression that Ash even called it "cute", causing the Water Pokemon to become embarrassed.
Trip eventually chose Snivy which caused Oshawott to become as still as a statue and fall over in shock. Oshawott, however developed an interest in Ash and left Juniper's lab, following the young Trainer from a distance. Oshawott later proved his worth by saving Ash's Pikachu and Iris's Axew from Team Rocket's clutches before fleeing the scene.
Oshawott finally showed himself to Ash and begged for Ash to take him along. Unfortunately, after attempting to capture Oshawott in a Poke Ball and failing, Ash realized that the Oshawott in question was the same one he had seen back at Professor Juniper's lab. Ash contacted Juniper who had become worried over Oshawott's mysterious disappearance and after getting her approval, obtained Oshawott's Poke Ball which gave Oshawott permission to fulfill his dream of travelling with Ash at last but Oshawott had gone missing again. After nearly falling into boiling water while stopping a dam from cracking, Ash saved Oshawott's life by returning the Pokemon to his Poke Ball, resulting in Oshawott becoming Ash's newest addition to his Unova team and also a permanent member of his overall team of Pokemon.
Oshawott is the first of all Ash's starters to not be caught after a Grass-type starter was captured (Tepig was second as always with fire types), Ash captured a grass-starter in each region first, then catching the other starters later on.
Besides Pikachu, Oshawott is the only other starter Ash got from a Professor. Ironically, Oshawott is the Water starter, which is what Ash wanted to start his journey with when he planned to pick Squirtle as his starter.
Oshawott seems to be over-confident, but at the same time scared of many things.
Though male, Oshawott's English Dub voice actor is Pokémon voice veteran Lisa Ortiz.
Oshawott can't fight well without his shell. This is probably because he uses it as a shield. This may also be because of one of his signature moves "Razor Shell", a Water-type move much the same as 'Razor Leaf'.
He has very similar personality traits to Dawn's Piplup and Ash's Gliscor, as Piplup can be spoiled at times and that Gliscor tries to get Ash's affection a lot and had a fear to overcome.