Basic Trope: Someone cool beyond belief who easily overshadows most everyone else, often also a main character, ends up biting the dust (relatively) early on the work's run time.
Straight: Garret Redmond is the strongest, fastest, wittiest, most inspirational, most resilient and the most unflinching expert swordsman with inner peace that would make Buddha blush of envy. He wears an extremely cool-looking armor and has a smile that gets women horny and men to faint. He offers Simon Drake, the protagonist, insights and advice that helps the latter immensely on his journey. Unfortunately, because he constantly makes the rest of the cast pale through no real fault of his own, an author, unless he wants the story he wants to tell to drown under the flashy show of Garret's coolness, has no choice but to kill him off.
Exaggerated: Take the above and add that he also tends to fight whole legions of soldiers, demons, aliens and dragons. He also often has passionate, steaming hot sex. Sometimes at the same time, during, before or after. He can make speeches that cause anyone who hears it to become ferociously enthusiastic. He can lower taxes just by willing it to happen and can bend the most twisted bureaucracy straight. He can jump so high he can easily cling to a jet flying nearby and get quickly to wherever he wants to go. Sometimes he does all of these at once. He dies during his first appearance in a shower of nuclear missiles.
Downplayed: Garret excels in many things, although it's far more subtle and only obvious when you think about it a little. He is the first (if not only) main character to die, but he lived for more than half of the story.
Garret has done lots of work and applied himself like mad, with lots of great teachers, opportunities and luck along the way. Someday, that luck would have to run out and bring him down to mortal.
Garret discovered a Divine Cheat Code to Reality. Rediscovering it is a story's driving force and thematic element because it was fixed and the fix caused his death.
Garret is literally not human. He's a paragon of many things people admire gained sentience, which is sent down to earth by a deity with his/her/its own motivations, who eventually "kills" and takes him back.
It happens in Simon's head. In this fantasy Garret is a personification of all Simon wishes he was. Garret's death is a sign for Simon to wake up.
Garcy is so unbelievably lame he makes everyone around him look cool, so repulsive in personality he drains energy from everyone else merely by being around them and a reminder of everything we don't want to be, but just won't die no matter how injured he becomes.
Garret becomes Out of Focus, but is still alive, despite having been through enough to have killed off most people, because he's too cool to die.
Garret is too lame to live.
Garret faked his death.
A bomb is thrown at Garret, and everybody expects it to be the end of him. He walks out of the explosion calmly.
Double Subverted: ...Only to be shot dead moments later.
Parodied: Any character even remotely cooler than The Hero (or who even looks cooler) inexplicable and instantaneously dies. As a result, he hangs out with a bunch of boring milquetoasts.
Zig Zagged: Garret has the ability to come Back from the Dead, but only under certain circumstances. He dies several times throughout the story, and neither the characters or the audience can ever be sure if and when he will come back.
Garret has many strengths, is interesting enough as a person and doesn't mind not being indulgently cool, and still dies first.
Garret is too cool to die.
Defied: The author decides to make Garret only somewhat cooler than the other characters, and/or lets him live long.
Discussed: The Mentor (or Genre Savvy Garret) tells Simon not to rely on Garret so much because of this trope.