25. Mon-El
Arriving in a pod at the conclusion of Supergirl‘s first season, Mon-El of Daxam went on to play a rather substantial role in Seasons 2 and 3.
A prince of his home planet, Mon-El was once used to being treated like royalty. However, on Earth, he came across as nothing more than a super-powered alien with a superiority complex. That is, until Kara made him see things in a different light. Perhaps for the first time in his life, Mon-El experienced real love, and it ultimately made him a much better person. Learning how to use his abilities for good, he began to behave like a hero, saving people and stopping major threats – even his own Daxamite parents.
After being sent into space, he accidentally ended up traveling through time into the future, where he became a member of the Legion of Superheroes – alongside his wife Imra and Brainiac 5. He then inadvertently returned to the present, reuniting with his old flame, Kara. Though he would question his feelings for both her and his wife during this period, it was actually during this stint on the show that the writers got to showcase his character growth as Mon-El showed Kara how much he had learned from her.
Mon-El’s journey on Supergirl is one of the best cases of character development we have seen in the Arrowverse. He went from a rich and entitled punk to a selfless, loving and inspirational hero. Through great material and a strong performance from Chris Wood, his progression felt incredibly natural and extremely well-paced.