Misty

Misty was a former travelling companion of Ash who traveled through the Kanto and Johto regions with him and Brock.

History
Misty was mentioned by Ash whilst on his date with Mallow in "Time Flies".

She made her first physical appearance in "Ash Ketchup Remembers Charizard", where she is seen travelling with Ash and Brock.

Trivia

 * Misty, along with Max, Cilan, Clemont and Bonnie where the only previous travelling companions of Ash to not appear in "Time Flies"