Ash originally obtained it as a Krabby in Mystery at the Lighthouse, where he caught it on a beach without engaging it in a proper Pokémon battle. Having six Pokémon already in his party at the time, the newly caught Krabby's Poké Ball was teleported away, much to Ash's surprise and concern. He soon learned that Krabby was sent to Professor Oak's, where it was dwarfed by an impressively large Krabby caught by Gary.
Although Ash was at first concerned that Oak might make a meal of it, Krabby soon became a usual sight for Ash whenever he made a video-phone call to Oak. It was not uncommon to see it assisting Oak in some manner, such as retrieving a phone or helping write poetry.
Krabby's battling debut came in Round One---Begin!, when Ash used it during the first round of the Pokémon League against Mandi and his Exeggutor. With a stroke of beginner's luck, Krabby defeats the Exeggutor and begins to evolve into a Kingler, finishing the rest of the match by single-handedly defeating Mandi's Seadra and Golbat.
Following the Pokémon League, Kingler would spend most of the time at Oak's lab as Ash and his friends traveled the Orange Islands and Johto. Ash used it in Johto during the Whirl Cup tournament, using Kingler in The Perfect Match his match against Misty and her Poliwhirl and Psyduck. Ash was going to use Kingler in the Johto League Silver Conference, but it was injured while rescuing a group of runaway Voltorb and he thus used the returning Squirtle instead.
Kingler currently resides at Oak's Lab.