Hartley Sawyer makes his first appearance as Ralph Dibny, a.k.a. the Elongated Man, in the October 31 episode of The Flash.
The episode is called “Elongated Journey Into Night” and here’s the write-up that The CW just released with some new spoilers:
TOM CAVANAGH DIRECTS; DANNY TREJO GUEST STARS AS BREACHER — Cisco (Carlos Valdes) is shocked when Gypsy’s (guest star Jessica Camacho) father, Breacher (guest star Danny Trejo), shows up on Earth-1. Breacher takes an immediate disliking to Cisco and decides to hunt him. Meanwhile, Barry (Grant Gustin) runs into his old nemesis, Ralph Dibny (guest star Hartley Sawyer). Tom Cavanagh directed the episode written by Sterling Gates & Thomas Pound (404). Original airdate 10/31/2017.