Flounder is a major character in Disney's 1989 animated film The Little Mermaid. He is Ariel's best friend, who
regularly embarks on her adventures despite his cowardly demeanor. Though his name would imply otherwise, he is not a flounder, but a tropical fish.
Flounder comes from a large family, with numerous siblings. His actual name, according to "The Evil Manta", is Guppy Number 35. His exact age is unknown, but he appears to be younger than Ariel (16) during the events of The Little Mermaid and its prequel stories.
There are two conflicting portrayals of how Flounder and Ariel first met. In "The Evil Manta", Ariel encountered Flounder during a swim, but her size made him believe she was a big fish trying to eat him, and thus swam off. After catching up to Flounder as he cowered in fear, Ariel explained that she was a friendly mermaid. Ariel offers to return Flounder home, to which he happily accepts. The two formally introduce themselves to each other and talk about their mutual interests while swimming back, cementing their friendship.
In Ariel's Beginning, however, Ariel overheard Flounder making music (which at the time, was forbidden by order of King Triton). When Ariel tries to join in on the fun, he and Ariel are confronted by guardsfish. Flounder leads Ariel to an escape while teaching her various fishing techniques. They are eventually confronted by Sebastian, who orders for Flounder's arrest for breaking the law. Ariel successfully vouches for Flounder's freedom, allowing him to go free.
Since their initial meeting, Flounder and Ariel developed a strong friendship. The two are nearly inseparable, to the point where Flounder is a welcomed guest of King Triton's palace and regularly participates in activities of the royal family. Being as how they spend nearly every moment together, Flounder also acts as Ariel's confidant. Ariel is also very protective of Flounder, at times acting as something of a mother figure to him. When the two find themselves in peril, Ariel will always put his safety before her own.
As her closest friend and confidante, Flounder is incredibly loyal to Ariel, as well as protective. Part of his reasoning for joining her various exploits is to watch out for her should things go wrong. Though he would rather her hobbies were less perilous, Flounder will always stick up to those who chastise Ariel for her adventurous spirit, including King Triton.
Flounder is essentially the polar opposite of Ariel. He is often riddled with anxiety, scares easily and hates adventure (for the most part). Like Sebastian and King Triton, Flounder is something of a "voice of reason" as he tries to talk Ariel out of adventuring for her own (as well as his) safety. Unfortunately, Flounder's apprehensions never get through. When gets "cold fins", in fact, Ariel will sometimes (and effectively) pressure Flounder into tagging along. While he is not necessarily insecure or prone to peer pressure, Flounder does not liked to be called "a guppy" (a baby, in underwater speech), and will therefor join Ariel on her forbidden exploits to prove himself. However, Flounder can be brave and pull through when Ariel truly needs him. For example, during the final confrontation with Ursula in The Little Mermaid, Flounder jumped into the battle by taking on Flotsam and Jetsam.