A team of ex-superheroes is forced to team with their arch-nemesis (who killed their mentor.) in order to fight a threat to big for any of them to handle alone . Ed Harris stars as Ion Garret.
- Ed Harris as Ion Garret, a super-powered criminal mastermind who re-forms the team he sought to destroy in order to fight a greater threat. He is able to manifest drawings into reality and is the show's main character.
- John Barrowman as Daniel Adams, the field leader of The Guardsmen. He can absorb and channel energy.
- Eva Mendes as Natalie Parin, the only female member of the Guardsmen. She can control light and darkness.
- Chris Pine as Rory Markus, Daniel's rival who can create 24 hour clones that each have a different power that he isn't aware of until after it's created .
- Matt Bomer as Eben Brooks, a telepathy-weilding womanizer.
- Idris Elba as Cooper Lee, an ex-mobster who has power-sapping and strength-stealing abilities.
- Kunal Nayyar as Ari Hudon, a geek who was obsessed with METAs. In an accident, he gained shape-shifting abilities and joined the team a few episodes into Season 1.
- Alan Rickman (flashbacks) as Cyrus O. Krane, the team's mentor who had control over time, but was killed by his nemesis, Ion Garret.
- Tim Curry as Jonathan Waylons/The Surgeon, as Jonathan Waylons he is the Speaker of the House and is promoting an Anti-META agenda. As the surgeon, he runs an unauthorized organizaton that splices META DNA. He is the main antagonist of Season 1. Note: When he wears the Surgeon mask, he is voiced by Ron Perlman in order to disguise his identity.
Introduced in Season 2
- Martin Freeman as Hamish Andrews, a META who was blackmailed into working for The Surgeon, but now has become a member of the Guardsmen. He ca control gravity and create portals.
- Peter MacNicol as The Eye, a mysterious super-intelligent sadist. He has the power to "hack" into any computer system or human mind, but this leaves him physically vulnerable. He is the main antagonist of Season 2.
In the present day, a select group of humans (called "METAs") had a special gene endowing them with powers. Many kept their powers secret but a few select METAs, who were mentored by the time-altering Cyrus O. Krane and led in the field by energy-absorbing Daniel Adams, fought crime as The Guardsmen. However, when Cyrus was killed by his archnemesis Ion Garret, the Guardsmen disbanded. 10 years later, in 2025, Ion must convince the ex-members to rejoin under his leadership in order to defeat a criminal mastermind known only as The Surgeon.