Originally, The Atom was a non-super powered hero from the 1940s, and a founding member of the Justice Society of America where he palled around with the likes of the Golden Age Flash, Green Lantern, Hawkman, Sandman, and more. Following the success of the Silver Age versions of The Flash and Green Lantern, characters still being used in comics and other mediums today, DC wanted to recreate The Atom. Ray Palmer was created by Gardner Fox and Gil Kane and made his debut in Showcase #34 in 1961. Unlike his predecessor, Palmer's character was given the ability to shrink down to microscopic sizes via a suit he created.

Eventually Palmer didn't need his suit to shrink or grow anymore, as the powers were retconned to simple be his own. The character would go on to star in a number of comics titled Sword of the Atom where he remained at his microscopic size and protected a tribe of tiny humanoids, think Conan the Barbarian meets Fern Gully. During his career, Palmer also became a member of the Justice League where he would meet one Carter Hall aka Hawkman, who would go on to become one of his best friends.

In DC's Legends of Tomorrow, Palmer is played by former Superman Brandon Routh. There were some changes made to the character's origins, namely that he was driven to build his ATOM suit by the death of his fiance and that initially the suit was designed for flying and shooting pulse beams than shrinking, a development that came later.

There have been many different iterations of Hawkman throughout comics, but the original version created by Gardner Fox and Dennis Neville made his debut in Flash Comics #1 in 1940. An archaeologist working in a museum, Carter Hall discovered not only that he was the reincarnated Egyptian Prince Khufu but that he could harness the powers of Nth Metal to defy gravity as Hawkman. As part of his visions of the past, Hall sees that his lover was one Princess Chay-Ara and realizes she too has been reincarnated when he meets a woman named Shiera the next day.

Much like The Flash, Green Lantern, and The Atom, Hawkman was reinvented during the Silver Age as Katar Hol, this time a fierce warrior and police officer from the planet Thanagar. He was partnered up with rookie cop named Shayera Thal and the pair eventually fell in love. After traveling to Earth to apprehend a criminal, the two decided to remain on the planet and adopted the names Carter and Shiera Hall.

Falk Hentschel will play the role of Hawkman in the upcoming series, having made his debut already in Arrow and The Flash. This version of the character will take his cues from the original version of the character, though the one change in their origin has them being originally killed by Vandal Savage and not Hath-Set.

The golden age version of Hawkgirl, Shiera Sanders, took on the identity of the hero after masquerading as Hawkman and later having her own wings created by Carter Hall. Both characters were members of the All-Star Squadron and it was later retconned that Hawkgirl was a full member of the Justice Society of America, though the character made few actual appearances with the group during the original run.

The third version of Hawkgirl to exist was a young woman named Kendra Saunders. After Kendra committed suicide and her soul left her own body, the soul of Shiera Sanders entered and took her place. As a result, she maintains all of Kendra's memories but none regarding her past lives with Carter, who finds this all very frustrating.

Ciara Renée takes on the role of Hawkgirl for DC's Legends of Tomorrow which is primarily based on the Kendra Saunders version of the character albeit with none of the soul-swapping with Shiera Sanders. Instead, Kendra is the reincarnated version of Princess Chay-Ara but still has no memory of her past lives or abilities until she had an awakening prior to their showdown with Vandal Savage.

Created by Jack Miller and Ruben Moreira in 1959, Rip Hunter was originally just an adventurer who created The Time Sphere which allowed him to travel all across time. The character eventually found himself teaming up with “The Forgotten Heroes,” a team of heroes that included Animal Man, the Suicide Squad's Rick Flag, Jr., and even Superman. As a result of the world-changing “Crisis on Infinite Earths” event which reset the continuity of DC Comics, Rip Hunter found himself as a literal man out of time, his home world totally erased with no one having any memory of him before.

A new version of the character premiered in the Post-Crisis continuity of DC Comics where he continued his life as a time-traveling adventurer. The character spent most of his time trying to prepare for the inevitability of attacks from other time travelers and as a result never disclosed his true identity. Rip went on to befriend another famous time-traveling hero, Booster Gold, who it was later revealed was Hunter's father.

In the series, Arthur Darvill will play the role of Rip Hunter, who has come from the future and assembled the team to put a stop to Vandal Savage, who has conquered the world in the year 2166. The character already has intimate knowledge of what will happen in the future as well, since the title for the series comes from his line of dialogue: “In the future none of you are heroes, you're legends.”

Like many other heroes, there have been a number of different versions of Firestorm in the pages of DC Comics. The first was created by Gerry Conway and Al Milgrom and saw high school student Ronnie Raymond and physics professor Martin Stein fuse together to form “The Nuclear Man.” Their powers included flight, fire fusion energy from his hands, and even rearranging the molecules of his surroundings to create other elements. Though Ronnie Raymond's body was the vessel for the character, Professor Stein's mind was still inside and offered advice to the character throughout their adventures.

Later another version of the hero existed, after Ronnie Raymond had flown around as the fire elemental for many years, wherein Raymond was fused with a new character, Jason Rusch. The pair eventually separated thanks to a particle created by Martin Stein, allowing both of them to be Firestorm simultaneously.

Though Robbie Amell appeared as Ronnie Raymond in The Flash, DC's Legends of Tomorrow will see a wholly original Firestorm with the inclusion of Franz Drameh as Jefferson "Jax" Jackson. Victor Garber will also reprise his role of Martin Stein for the hero's role in the series.

Though a character called the White Canary has previously appeared in DC Comics, she holds almost no relation to the character that will be seen in the series. In the source material, White Canary was a member of the Twelve Brothers in Silk, a family of killers, who adopted the name as a means of taunting the Black Canary (Dinah Lance).

In the series, Caity Lotz will reprise her role of Sara Lance. Having previously worn the identity of the “Canary” in the series and then being resurrected from the dead, she will take on the identity of White Canary. The last we saw of the characer she had fled Star City to try and gain control of her bloodlust, so it's unclear where the character has gone or where we will find her at the start of “Legends.”

Created by John Broome and Carmine Infantino, Leonard Snart was once a small time crook put away by The Flash after a robbery gone wrong. Hoping to continue his life of crime but deciding he needed to do something about the Scarlet Speedster, Snart designed a weapon to stop The Flash in his tracks and broke into a laboratory to get a crucial element. The weapon, however, did something unexpected and froze the air around it when fired. Snart adopted the name Captain Cold as a result and continued his life of crime.

Snart has always been a thorn in the side of The Flash, and not just the Barry Allen version of the character. He also fought against the third Flash, Wally West, and even killed the fourth flash, Bart Allen, with his fellow Rogues. The character is most well known for his cold gun and his signature blue parka.

Wentworth Miller will return as Leonard Snart in DC's Legends of Tomorrow, reprising his role from The Flash. Though the character maintains his bad streak, he has been seen in recent episodes to have a good side, going so far as to warn Barry Allen about other villains' plans. Perhaps his heroic side will fully emerge in the series.

Heat Wave, aka Mick Rory, first appeared in The Flash #140 in 1963, also created by John Broome and Carmine Infantino, as a pyromanaic that carried his own flamethrowers. The character is primarily a villain of The Flash but also a rival to another Flash villain, Captain Cold. Having a staunch fear of the cold, the pair butted heads with some frequency before finally becoming allies.

The most recent version of the character as seen in DC's “New 52” no longer required flamethrowers, instead having pyrokinetic powers himself. He maintained his obsession with fire in the line wide relaunch.

Dominic Purcell will reprise his role of Heat Wave from The Flash in DC's Legends of Tomorrow which should prove to be an interesting addition to the team as the only outright villain, because even Captain Cold has previously flirted with doing the right thing in the series.

As old as time itself, Vandal Savage is an immortal villain that has conquered and terorrized parts of the world for centuries, going by many different names including Alexander the Great, Julius Caesar, Genghis Khan, Blackbeard, Vlad the Impaler, and even the notorious Jack the Ripper. The character has faced off against nearly every hero in the DCU from Green Lantern to Batman and even the prehistoric version of the caped crusader.

Danish actor Casper Crump will play the role of Savage in DC's Legends of Tomorrow whose origin has been slightly combined with Hath-Set from the pages of Hawkman comics. The character was defeated by the Green Arrow and The Flash in this year's crossover episode and left as a pile of dust; however, the new Ra's al Ghul (Malcolm Merlyn) scooped up his remains and took them away to parts unknown, presumably to resurrect him.