Michael Emerson has been cast for the sixth season of “Arrow.”

Emerson – known for his roles as Ben Linus in ABC’s “Lost” and as Harold Finch in CBS’ “Person of Interest” – will have a recurring role as an unnamed mystery character.

The “Arrow” panel at San Diego Comic-Con on Saturday also announced that fan-favorite guest star David Nykl, who plays Oliver’s Russian friend-turned-nemesis Anatoly Knyazev, will also be returning for Season 6. Oliver and Anatoly departed on rocky terms the last time the two saw each other in Season 5.

“Arrow” returns for its sixth season on Thursday, Oct. 12.

“The Flash” also announced that they have cast Danny Trejo, Neil Sandilands, and Kim Engelbrecht for the CW show’s upcoming fourth season.

Trejo — known for roles in films like “Machete,” “From Dusk Till Dawn,” and “Spy Kids” — has signed on to play the role of Breacher, a feared bounty hunter from Earth-19 and the imposing father to inter-dimensional bounty hunter, Gypsy (Jessica Camacho). His mission is to prevent any inter-dimensional traveler from threatening life on his planet, especially his daughter’s.

Sandilands will play DC villain Clifford Devoe, aka The Thinker, a metahuman with a mega mind who embarks on a season-long battle with The Flash that pits the “fastest man alive” against the “fastest mind alive.” A true genius, he’s devised an intricate plan to fix all that he deems wrong with humanity.

Engelbrecht has been cast as DC character The Mechanic, a highly intelligent engineer who designs devices for Devoe. As Devoe’s right hand, she’s the truest of true believers who’ll stop at nothing to help him implement his plan to fix humanity.

The Flash returns for season four on Tuesday, October 10, at 8/7c on The CW.

James Remar and Damon Gupton are also joining the cast of the CW’s “Black Lightning” as series regulars.

Remar (“Dexter,” “The Warriors”) will play Peter Gambi, the oldest friend to main character Jefferson Pierce (Cress Williams). Gambi is described as Jefferson’s father figure, mentor, and “tailor” and their relationship will become a painful window into the past.

Gupton (“La La Land,” “Bates Motel”) will play Inspector Henderson. As a veteran law officer, Henderson and Black Lightning are at odds, but soon become unlikely allies.

“Black Lightning” is set to debut in 2018.

“DC’s Legends of Tomorrow” is also bringing back some familiar faces for its upcoming third season.

Neal McDonough, Wentworth Miller, and Arthur Darvill will all be reprising their roles from previous seasons.

McDonough returns as a series regular, reprising his role as the villainous and mystical Damien Darhk. Darhk appeared in Season 2 of “Legends of Tomorrow” alongside Eobard Thawn (Matt Letscher) and Malcolm Merlyn (John Barrowman) as a member of the Legion of Doom. McDonough first appeared as Darhk as the primary antagonist during the fourth season of “Arrow.”

Miller will return as Leonard Snart, aka Captain Cold, in a recurring role. Snart first appeared in Season 1 of “The Flash” before becoming a full-fledged member of the Legends of Tomorrow during the show’s debut season. Seeing as how Snart sacrificed himself at the end of “Legends” Season 1, it will be interesting to see how the character returns.

Darvill will also return as a recurring guest star for the third season as Rip Hunter. Hunter was the Time Master responsible for bringing the Legends together in the first place. Season 2 last saw Hunter exiting the Waverider to blaze his own trail.

“Legends of Tomorrow” returns to the CW on Tuesday, Oct. 10.

Adrian Pasdar, Carl Lumbly, Emma Tremblay, and Yael Grobglas have also been cast in “Supergirl” Season 3.

Pasdar will play Morgan Edge, a ruthless real estate developer who will stop at nothing to get what he wants. The DC villain’s big plans for National City instantly put him at odds with Supergirl (Melissa Benoist) and Lena Luthor (Katie McGrath).

Lumbly will play M’yrnn J’onzz, the father of J’onn J’onnz, the Martian Manhunter (David Harewood). A pacifist religious leader on Mars, M’yrnn pushes his son in unexpected ways. Lumbly previously voiced the Martian Manhunter on the “Justice League” animated series.

Grobglas will portray DC character Psi, a psychic villain who uses people’s own minds against them.

Tremblay will play Ruby, a smart, independently-minded National City kid who’s fascinated by Supergirl and ends up in jeopardy because of it.

Supergirl returns for its third season Monday, Oct. 9, at 8 p.m. ET on The CW.