4. Supergirl (Kara Zor-El)
For twenty one non-comic book years, Superman was billed off and on as the last survivor of the doomed planet of Krypton as long as Kandor, Krypto, and the Phantom Zone villains were not needed to provide some Silver Age zaniness. That changed in Action Comics #252 in 1959 when Big Blues cousin, Supergirl, made her first in-continuity appearance. The Maid of Steel was a popular enough character even though she never held down a solo title very long but she was more than just a trademark holder for DC as proven by her cross media appeal of giving young females in a less liberated day a super character to call their own. She never seriously rivaled Wonder Woman for the title of Queen Bee when it came to comics but she was just as recognizable as Batgirl, Catwoman, and Wonder Girl which means she was popular indeed. Popular enough to get the big screen treatment in 1984 which is something not even Princess Diana has been able to swing as of this date. Yeah, popular enough but not so popular that DC could get away with killing her off when her death was demanded by editorial dictate to Marv Wolfman and George Perez during the great housecleaning that was Crisis on Infinite Earths. It was decided Superman needed to truly be the sole survivor of Krypton again when the DCU was rebooted after Crisis so that he was unique among all characters of his continuity as truly the last of his kind. So Kara gave her life in battle against the Anti-Monitor, the villain of the piece, to save her cousins life in issue seven of the series in a story that was as heart-rending as its cover of a grief-stricken Kal-El with tears streaming down his face holding his cousins lifeless body with an almost countless number of heroes gathered from DCs various eras mourning in the background. Mission accomplished and Superman was once again the last of his kind as Supergirl exited the stage in a manner befitting a true heroine.
IMPACT: Kara Zor-El died and outside of a few supernatural visitations she stayed dead but the Supergirl concept bounced around DC for almost twenty years in the form of clones, doppelgangers, and even an angel None of them seemed to stick outside of Power Girl, the cousin of the Golden Age Superman, who had a totally different vibe than her counterpart and already existed pre-Crisis. Characters in comics are never totally abandoned especially ones with the powers of the original superhero wont stay down forever and so it was for Kara who was given a second life in 2004 in Superman/Batman #8 by Jeph Loeb and Michael Turner in an arc called simply Supergirl. That second life has paid off for her and her publisher with the character now being an integral part of the modern DCU in the pages of her own successful solo book and a shining example of female empowerment in the wider culture as seen by all the young ladies wearing Supergirl tees on hot, summer days.
OPINION: Some have said Kara Zor-El dying was the best thing to ever happen to the character and I would have to agree even though I wasnt a big fan of re-introducing the concept of Supergirl as a mass of protoplasm from an alternate universe by John Byrne in his rebooted Superman stories shortly after the original expired in Crisis. Supergirl should have stayed dead with Kara Zor-El because she was the only one the public responded to in that persona but what are comics if not cluster screws because DC went around the universe and back only to discover nothing beats the original which is why the character is so well-loved today.