"There he goes. One of God's own prototypes. A high-powered mutant of some kind never even considered for mass production. Too weird to live, and too rare to die."
— Hunter S. Thompson, referring to his Hetero Life Mate, Oscar Zeta Acosta.
Let's say a character is a Ninja Pirate. Let's say he also has a giant robot. Let's say that giant robot also has an Infinity+1 Sword. Let's further say that said sword is actually a katana. No, make that a chainsaw katana. Hell, let's say it's two chainkatanas... attached by a chain to make chainkatanachucks.
Clearly, this character is Made Of Cool. Equally clearly, this character, if he is not the Main Character, must die, because he overshadows the main character.
This is what happens when somebody is Too Cool to Live.
This character is often relegated by The Plot Reaper to the job of being a Heroic Sacrifice, or the Sixth Ranger. Many a wise and awesome mentor has fallen victim to this trope.
Sometimes, a main character is Too Cool to Live, and so performs a Heroic Sacrifice at the end of a movie or television series. Apparently there was just no bus service in the area.
Sometimes results in a Disney Death due to Executive Meddling if the character is popular enough, but usually only if they Never Found the Body.
Alternatively, this character doesn't die, but is removed from the stage in some way. Or he turns evil, and his superior coolness is put to use as an obstacle for the hero to overcome. And we all know that Evil Is Cool.
It may be justified as it allows the next generation, mainly the hero, to improve greatly to make up for the loss of this person.
See also Too Good for This Sinful Earth - a character who is just too gentle to stay in the story and Too Powerful to Live - a villain who is just too dangerous thanks to his Story Breaker Power. Also tends to cross over with The Obi-Wan. Many Crutch Characters in video games channel this trope. Compare Too Happy to Live. When this is about works rather than people, it's Too Good to Last.
Compare Dying Moment of Awesome.
Being Too Cool to Live can be very subjective, so please try not to Edit War. Also: since this is a death-related trope, Here There Be Spoilers.
You have been warned.