Connor MacLeod from Highlander.

Born in 1518, he is an Immortal, doomed to walk the Earth and watch everyone he loves grow old and die — but eventually, he must battle the few other remaining Immortals for the Prize. And in the end, wait for it... there can be only one.

Captain Jack Harkness from Torchwood.

He's just your average run-of-the-mill con man from the 51st century, until he dies, and the temporarily all-powerful Rose Tyler brings him back to life. Only now, he's a "fixed point in time and space," eternally young and invulnerable forever, no matter what. His wife dies of old age, his daughter is the same age as him, and eventually (maybe) he'll be just a head in a giant jar.

Jenny Sparks from Stormwatch and The Authority.

Born in 1900, she stops aging when she reaches her 20th birthday. Maybe its to do with the fact that she's a being of pure electricity. In any case, she befriends Hitler, visits an alternate universe where she marries an alien prince, and finally gets to join two of the Wildstorm Universe's biggest super-teams, until she finally dies at age 100.

Wolverine, from the X-Men.

Logan used to be just a guy with a tremendous healing ability, but recent comics (and his new movie) revealed that he's actually ageless, and fought in the Civil War and every big war since then. He can smoke as many cigars as he wants, and he never gets weird cigar-related wrinkles. Various comics have shown him surviving long past the end of the world, or at least vastly outliving all his compatriots.

Enoch Root in Neal Stephenson's Baroque Cycle and Cryptonomicon.

One of the great mysteries of Cryptonomicon was how Enoch Root managed to show up, hale and hearty, 55 years after he dies in 1945. We eventually do learn that Root has the secret of rejuvenation, which he uses to keep himself (and sometimes others) alive.

John Carter of Mars, from the novels by Edgar Rice Burroughs.

Even before he gets whisked off to Mars, aka Barsoom, he's mysteriously gifted with eternal youth. And no matter how many times they try to kill him, he always comes back. (Although sometimes, he comes back on Earth instead of Barsoom.)

Nick Fury and (maybe) his Howling Commandos, from Nick Fury of S.H.I.E.L.D.

Nick Fury (the comics version, not the movie version played by Samuel L. Jackson) fought in World War II, where he gave his eye for his country. But he's miraculously still young and spry in the present day — and he didn't get frozen in an iceberg, like Captain America. Instead, Nick Fury got exposed to something called the "Infinity Formula," and (at least in some versions) so did his men, including "Dum Dum" Dugan — who's now been going by "Dum Dum" for 70 years.

Lazarus Long, from Time Enough For Love by Robert Heinlein.

Born in 1912, Lazarus Long is the third generation of a selective breeding experiment by the Ira Howard Foundaiton, so he lives for nearly two thousand years in good condition — with only the occasional rejuvenation treatment required. And he eventually finds out that he actually can't die.

Claire Bennet, from Heroes.

The cheerleader doesn't really seem to need saving — it turns out that even scooping her brains out can't kill her, and it's been hinted she'll stay young and healthy forever. At least, Sylar believes that hundreds of years from now, only he and Claire will still be running around, and eventually they'll fall in love. Or something.

Richard Alpert, from Lost.

Is he a hero? We're still not sure. He's definitely taken part in some questionable decisions, but who hasn't on this show? In any case, he's mysteriously ageless, whether we see him in 1954 or the present day. Here's hoping we find out his secret this coming season.

Runners up: Superman (who ages in some versions but not in others), Kane from the sword-and-sorcery novels by Karl Edward Wagner, Wonder Woman, Samantha from Bewitched, Dorian Grey, The Endless from Sandman, Thor, Takeshi Kovacs from Richard K. Morgan's novels, John Amsterdam in New Amsterdam, Peter Pan, Earthworm Jim, Aes Sedai from the Wheel Of Time, Kai on Lexx, and a host of robot/cyborg characters.

Additional reporting by Alexis Brown. Thanks also to Matt Jones, Ron Hogan, Ekaterina Sedia, Jason Shankel, Missy Feigum, Hiya Swanhuyser, Victor Infante, Jefferson Robbins, Jessy Randall, Stephen Tiano, Becka Robbins, Jennifer Brissett, Ashley Edward Miller, Andrew Liptak, Paul McEnery, Ryan Britt, Yoz Grahame, Shannon Rosa, Espana Sheriff, Lisa Heselton, Lane Kneedler, Naomi Alderman, Darren McKeeman, Robert Hewitt Wolfe, Shane O'Brien, Hanne Blank, Lucas Zen Hannon, Mariah Bear, Lun E'Sex, Micky Shirley, Swill Magazine, and anyone else I forgot!

Scientists say that aging bodies release an enzyme called collagenase that literally eats away at collagen, which in turn makes the skin weak and thin. It sags and becomes easier to bruise or tear. If collagenase could be removed from the body, or the collagen itself rejuvenated, people's skin would stay firm and healthy. There are several possible substances already available that could promote collagen regrowth (you can see one, Restylane, plumping up collagen in the image above).

According to Eurekalert:

The U-M researchers base their conclusions on past studies in which they have explored why certain anti-aging treatments are effective. A 2007 study looked at Restylane, marketed as a dermal filler, and found that injections of the product caused fibroblasts to stretch, promoting new collagen, and also limited the breakdown of collagen.

In another 2007 study, the U-M team tested lotions containing retinol, a form of Vitamin A found in many skin-care products, and found it significantly reduced wrinkles and skin roughness in elderly skin by promoting new collagen. Other U-M studies have shown why some laser treatments work and some less powerful ones do not. Carbon dioxide laser resurfacing is effective because it removes the aging dermis; in the three-week regrowth process, new, young collagen is produced.

Voorhees and his colleagues say they provide needed, independent research on the effectiveness of available and future treatments to counteract skin aging. They have no ties to the manufacturers of products they study.

It sounds like the early twenty-first century may be the first time in human history when you might have no idea how old the person is that you're talking to. With collagen replacement, you might think that you're dating a 25-year-old until she suddenly drops dead of old age.

Why Some Treatments Rescue Aging Skin [Eurekalert]