It looks like tonight we will be introduced with the CWverse version of Cyborg Superman. There has been a lot of talk about who it will be since the normal alter ego of Hank Henshaw is now J'onn J'onzz, The Martian Manhunter… but I'm sure David Harewood could play more than one part at a time. But let's take a look at the comic book history of Hank Henshaw / Cyborg Superman.
The first thing you need to know is that Henshaw was original created as a pastiche of Reed Richards. He, his wife Terri and two other astronauts on board the Excalibur are affected by the radiation of a solar flare and turned into a version of the Fantastic Four. But this version, upon returning to Earth, begin to deteriorate. Two members kill themselves, Henshaw is able to save his wife but he transfers his consciousness into the Lexcorp mainframe before his own body dies. Now in the computer, Henshaw is able to build himself a robotic body, but the sight of which pushes Terri into a bout of insanity where she takes her own life. Not the happiest story in the Superman line. Henshaw creates a small ship and flies off into space alone.
While travel in space… alone… Henshaw comes to believe that Superman caused the solar flare that affected his crew. Superman had been in a fight with a Kryptonian artificial intelligence called the Eradicator, who he threw into the sun. Henshaw's solitude lead to paranoia and a belief that Superman had cause the solar flare on purpose to take out the Excalibur. He eventually ended up on Warworld where he enlisted Superman's foe Mongul into a plan for revenge.
We would next see Henshaw during the Reign of Supermen. Superman is believed dead and four men step up in his place. Henshaw claimed to be the real deal, but his badly damaged body having been healed by technology. His plan involves taking out the Eradicator who is also posing as Superman and it allows Mongul to destroy Coast City… it's a major moment in DC History as it also leads to Hal Jordan becoming Parallax. Coast City was chosen because it's where Henshaw and his wife had lived and he was trying to erase his old life. The real Superman returns, teams up with a few other heroes to confront Cyborg. When Eradicator sacrifices himself to save the real Superman by stepping in front of a Red Kryptonite blast, it filters the radiation and restores Superman to full power, allowing him to defeat Cyborg Superman. (There's a lot more to Reign of Superman, you should read it.)
From their he teams up with Doomsday to plunder Apokolips with a new body that still retains the look and some power of Superman thanks to Henshaw having spent some time in Superman's birthing matrix. Henshaw is captured by Darkseid and put into a little orb to be used against Superman at a later date. Eventually Darkseid releases Henshaw who gets involved in a trial of Superman for the actions of his ancestors, but Henshaw betrays the tribunal and is sentence to death. But you can't kill his electronic consciousness which ends up heading over to the Marvel Universe.
He is pulled in by Thanos in the Green Lantern / Silver Surfer crossover where he tries to create a new Warworld only to be destroyed again… and later he tries to take over Kandor and ends up in the Phantom Zone. I guess they finally figured out the whole destroying his physical body thing wasn't working.
Over the years he would become the Grandmaster of the Manhunters, a member of the Red Lantern Corps and ended up working with the Alpha Lanterns in Brightest Day.
When the New52 came about, Hank Henshaw is not the Cyborg Superman… that turns out to be Zor-El who escaped Krypton and was turned into a cyborg by Brainiac. Henshaw is part of a 10 year mission to Jupiter that has an accident and when Superman is rescued, he is the only one on the ship. He returned with no memories of the trip and carrying part of the Oblivion Stone.
Henshaw has been quite a malleable character over the years. Starting off as a some what heroic clone of Reed Richards and then turning into an evil doppelganger of Superman and then being pulled into the Green Lantern stories as a powerful villain for events… but he hasn't really grown as a character since Reign of Superman.
How he will be used on Supergirl will be interesting to see. Will it be Hank Henshaw or another man and will they actually call him Cyborg Superman? If he doesn't look like Superman… then does the name make sense?