Kid Flash, Aka Wally West, in the season 2 (and at the time series) finale of Young Justice.

Wally was never my favourite character, especially not in season one, but he was an important part of the original 4 members of the team. And one of the best things season 2 did was deepen Wally's character through his interactions with Flash and Impulse, especially his final act in season 2.

Kid Flash got his powers by recreating Barry's science experiment, and because he didn't recreate it perfectly, his powers are weaker than the "true Flashes" like Barry and Impulse. He has trouble decelerating, needs to consume a lot of calories to run, and is not as fast. These shortcomings are sprinkled around the show, especially in season 2. All three Flashes respond to a super villain and Barry and Impulse are able to hold a conversation at super speed, while Kid gets "about every 5th word". Kid runs out of reserve "snacks" on his transcontinental run to deliver a transplant heart. Likewise due to a lack of snacks he is unable to carry Artemis to safety in Bialia.

Kid knows he is weaker than the true Flashes, but he never lets this get him down, he never uses it as an excuse, and he fights right along side them and along side his team every time heroes are needed.

This all comes to a head in the series finale when the three Flashes are counteracting a magnetic malestrom that will engulf the planet. Kid can't run as fast as the other two and so the storm zaps him with electricity as energy tries to escape their vortex. If Kid stops, two Flashes aren't enough to contain the storm, and so he chooses to keep running and dies in the process.

A sacrifice he only had to make because of the gaps in his power, but he embraces his fate for the survival of everyone he cares about.

His last words to Barry Allen: "Artemis [his lover] is gonna kill me for this. And don't even get me started on mom and dad. Just tell them, okay?"