Dory!
Dory is probably the most friendly and most sociable fish in the whole of the ocean. She loves talking to any fish and would love to tell them her life story, but she can't...Dory suffers from short term memory loss.
Dory helps Marlin on his quest to find his son, but at times, Marlin takes advantage of Dory and her memory loss, although after a while he does regret doing this as she gets physically hurt from him taking advantage. However Dory is always there for Marlin and comforts him when he becomes more and more upset.
Near the end of the film Marlin leaves Dory as he feels as if there is no point in continuing searching, but Dory carries on searching for Nemo. She is determined to find him and prove to Marlin that he shouldn't give up.
Eventually Dory finds Nemo and they then find Marlin together. Eventhough Nemo has no clue who Dory is, he soon gets to know her and they become great friends and she ends up living with Marlin and Nemo.