Syfy's series about Superman's grandfather is getting ready to go into production. We have the first character details here.

Announced back in December of 2014, Syfy's Kryptonwill take the Gothamroute, and tell a pre-Superman story. So if Smallvilledidn't go far enough back for you, Krypton should do the trick. Syfy has ordered a pilot that will be directed by Colm McCarthy, and written by David S. Goyer (Man of Steel) and Ian Goldberg (Once Upon a Time). Sleepy Hollow's Damian Kindler is on board as series showrunner.
Krypton TV Cast and Characters
Camerone Cuffe (who recently appeared in Florence Foster Jenkins) will play Superman's grandfather, Seg-El. Varietyhas some character details:
"Seg-El is the scion of the once prosperous El family and is blessed with an intuitive brilliance for all things technical. He is now living in Krypton’s lowest caste after his family was stripped of its rank."
In addition to Mr. Cuffe as Seg-El, Georgina Campbell will play Lyta Zod, who is, as you expect, an ancestor of Superman villain General Zod. According to Deadline, Lyta Zod "is a member of Krypton’s military caste and the daughter of a general, Alura Zod. Lyta Zod serves as a cadet — and has also been having a clandestine, forbidden romance with Seg-El (Superman's paternal grandfather)."
Ian McElhinney (Barristan Selmy on Game of Thrones) will play Seg-El's grandfather, Val-El. According to Deadline, Val is "a rogue genius who believes that space exploration is a basic form of self-defense, and he has tried, without success, to warn the Kryptonian elite about the arrival of an ancient threat." Could that be Brainiac? An earlier TV Line description said "Seg’s genius grandpa defied death by going into the Phantom Zone, and is a staunch believer in space exploration."
Elliot Cowan is Daron Vex, "the Chief Magistrate of Kandor. His real business is defending Krypton’s established oligarchy against heretics and dissidents."
Ann Ogbomo (World War Z) is Primus Alura Zod, "Lyta Zod’s mother and a leader of Krypton’s military guild. She is an extremely tough and demanding training officer."
Rasmus Hardiker (Your Highness) is Kem, "a brilliant engineer as well as Seg-El’s best friend and partner in an underground tech-repair business."
Wallis Day (The Royals) is Nyssa Vex, "a junior magistrate and the daughter of Daron Vex. Pierre is Dev-Em, a cadet under the command of Primus Alura Zod."
Aaron Pierre (Tennison) is Dev-Em, "a cadet under the command of Primus Alura Zod." Incidentally, Dev-Em is from the comics, and is one of the Phantom Zone criminals who periodically ends up on Earth to annoy Superman. Dev-Em was a background character in Man of Steel, for example.
(thanks to Deadlinefor the casting descriptions above)
We're still waiting on the casting of Ter-El, Seg-El's Great Grandfather.
Krypton TV Story
Here's the closest thing to an official synopsis we have right now.
Years before the Superman became a superhero, the House of El was shamed and ostracized. This series follows The Man of Steel’s grandfather as he brings hope and equality to Krypton, turning a planet in disarray into one worthy of giving birth to the greatest Super Hero ever known.
"It takes place 200 years before Man of Steel," Mr. Goyer told ComicBook.com at a press junket back in October. Whether he means it's actually intended as a prequel to the film version of Krypton remains to be seen. Warner Bros. has so far been cagey about crossing over their film and TV universes. It sounds possible, though, as Mr. Goyer also said they had "only scratched the surface" in the first act of Man of Steel.
We'll get you more on Kryptonas we hear it. We'll probably get news on whether the pilot is picked up by the end of the summer.