From Bulbapedia, the community-driven Pokémon encyclopedia.
Misty's Togetic (Japanese: カスミのトゲチック Kasumi's Togechick) was found as a Pokémon Egg by Ash Ketchum in Grandpa Canyon in EP046. Ash, Misty, Brock and Meowth fought over the egg and competed to determine who would be the eventual owner. When the Pokémon Egg hatched into Togepi, the first thing it saw was Misty, and it chose her as it's trainer, thinking that she was its mother. It ended up being the sixth Pokémon Misty got in the Kanto region.
Although Togepi appeared harmless, it sometimes used Metronome to get out of dangerous situations.
It evolved into a Togetic to defend the Togepi Paradise in A Togepi Mirage!, and left Misty to protect the Mirage Kingdom and the Togepi who lived there..