Marlin

Marlin is the protagonist of Finding Nemo. He will be returning in Finding Dory as the film's deuteragonist. He is Nemo's father who journeys to Sydney to rescue his son with some help from Dory.

Biography
"After losing his wife and family to the ocean, Marlin is left alone to raise his only surviving child, Nemo. He struggles with his inability to let go of Nemo as his son begins school. When Nemo is suddenly taken away by scuba divers, Marlin must try to find in himself the courage, wisdom, and faith needed to search the unpredictable ocean to bring his boy home - the very characteristics he needs to allow his son to learn and grow. Only then will he truly find Nemo."

Finding Nemo
In Finding Nemo, when Marlin's wife Coral and other unborn children were all killed by a barracuda, Marlin finds only one of his child egg. He names it Nemo, since that was one of the names his wife wanted to call one of her children. Through the years, Marlin has became overly protective over Nemo, much to the annoyance of Nemo. Marlin feels that the ocean is way too dangerous; he even doesn't want Nemo to go to school.

When Nemo gets captured by a pair of scuba divers (and after Nemo disobeys his father and swims up to a large boat known as a "butt" and touches it), Marlin risks everything to find his son and get him back. Along the way, he meets Dory who accompanies him on his journey.

After befriending some vegetarian sharks named Bruce (whom they first encountered), Anchor, and Chum, Marlin and Dory find a mask that Dory reads that says, "P. Sherman 42 Wallaby Way Sydney," but after reading the mask in another scene, a hungry anglerfish shows up, roars at Marlin and Dory, then chases after them. However, the duo manage to trap it by using the mask to tie it around a rock. Dory remembers what the mask says and on the way continues to repeat it until Marlin comes upon a group of Moonfishes and tries to ask them, but they only make fun of him, so Dory asks them for Marlin and they give them the directions to Sydney, to which Marlin thanks them. But unknown to the clownfish, the Moonfish also give Dory a warning not to swim over a trench. However, when Marlin and Dory reach the trench, Marlin makes Dory swim over a trench, much to her warning and they get stung by a group of jellyfish and knocked out. When Marlin wakes up, he finds that he's riding a sea turtle named Crush on the East Australian Current. Marlin asks Crush if Dory is okay and Crush points down to another turtle where Dory appears to be "dead". Marlin swims down to her, sees the scars on her side from the jellyfish stings, and blames himself for her getting hurt. But Dory wakes up from her "death" because she was playing Hide-and-Seek with the turtle kids. Marlin then tells Dory and the turtle kids about he and Dory's journey.

Later, after they left the East Australian Current, Marlin and Dory get swallowed by a whale, which was chasing krill.

Later on, when Marlin got sick of being stuck in the whale, he tried to break himself free, but fails, and he drops onto the whale's tongue, crying. Dory asks him if he's okay, but Marlin doesn't answer, so Dory swims down to him to comfort him and immediately says the same eight words "There, there. It's all right. It'll be okay" to do so. Marlin tells Dory his promise to Nemo, but Dory explains to her friend that he can't never let anything happen to him.

Finding Dory
Marlin is set to return in the upcoming sequel, Finding Dory.

Personality
Marlin was initially a very playful, happy, and easygoing clownfish as shown through the interaction with his wife. He was shown to be slightly lazy, as he wanted to name half of his children Marlin Jr. and the other half of his children Coral Jr. However, he was also shown to be very brave, as he attempted to defend his wife against the barracuda who sought to eat his children and his wife, but was ultimately repelled and knocked unconscious and into the sea anemone before he could do anything. This protected him, but also cost him his entire family, with the exception of Nemo, who was left with a crack in his egg, which could have caused his "lucky fin."

From this moment on, Marlin became overprotective, neurotic, paranoid, worrisome, and pessimistic, as he made several practices and conditions for Nemo and himself to follow to make sure they were protected and safe. He became paranoid and neurotic about any potential danger that could occur to Nemo and as such rarely left Nemo alone due to the traumatic experience of losing the rest of his family to a barracuda attack, and not wanting the same thing to happen to Nemo. However, this overprotectiveness is what put somewhat of a strain between him and Nemo, as Nemo felt suffocated and oppressed by it.

He also seems to, initially, be very serious, as shown when he couldn't tell a proper joke to some of Nemo's classmates' parents because he kept explaining obvious aspects of the joke, causing him to be considered unfunny despite the apparent notion that all clownfishes were supposed to be funny, which became a recurring gag throughout the movie as others state, "He's not very funny for a clownfish."

During his journey, Marlin was on the verge of losing Nemo, the only family he had left, and was rushing as fast as he could to save Nemo. This caused him to have little patience for Dory's antics and to other sidetracks.

However, despite these qualities, Marlin has proven to love his son more than anything and anyone in this world, and it is this love that fuels his determination, strength, courage, and bravery as he journeyed throughout the sea to find his son after he is kidnapped by humans. Marlin overcame with the bravery and courage not seen in his previous behavior to recover the person he loved most in the world despite the odds being against him.

Throughout the journey, he makes several friends and begins to understand that he should have given Nemo more freedom, particularly through his interactions with Dory and Crush because, as Dory states, "You can't let nothing happen to him, because then nothing will happen to him," meaning if Marlin doesn't let Nemo grow up and get out in the world, he won't be able to live life to the fullest.

He also begins to enjoy himself throughout his journey, and slowly sheds his serious personality, as shown when he had fun when he competed with Dory in racing to see who could get out of the jellyfish valley first and finally managed to have fun with his son Nemo by the end of the film.

Trivia

 * In Monsters, Inc., a painting of Marlin can be seen on the wall behind the Sushi Chef.
 * As pointed out by Nigel, a marlin is actually a type of billfish (such as the sailfish and the swordfish) that is popularized by sport fishing.
 * In reality, whenever a female clownfish within a school of fish dies, a male will change gender to make up for the death. Scientifically speaking, if Finding Nemo had been more accurate to nature, Marlin would have become female shortly after his wife's death. This would have made him Nemo's mother, not his father.
 * Marlin is the third protagonist to be turned into a deuteragonist in the second film. The first was Lightning McQueen from Cars 2, and the second was Sulley from Monsters University.
 * Marlin is the first Pixar protagonist to lose his love interest.