Says The Hollywood Reporter, "Valdes will play the series regular role of Cisco Ramon, a mechanical engineering genius and the youngest member of the team of scientists at STAR Labs. Born into a lower-income family, Cisco's brains and talent helped him reach his potential. He is loyal and eager and provides the comic relief in contrast to his stiff co-workers. Best part: He is as much of a comic book fanboy as Barry."
The comic book bit may be significant, given that in the original comic book source material, DC's Multiverse was born (or at least revealed) when Barry, a devotee of Golden Age comics who took on the name of The Flash, one of his favorite comic book heroes, on purpose, ended up discovering that Jay Garrick--the fictional Flash of his childhood--was actually not quite so fictional, but rather resided on an alternate earth.
The character's recent monthly comic book series began with DC Entertainment Chief Creative Officer and longtime Flash scribe Geoff Johns co-writing the series with The Flash and Arrow showrunner Andrew Kreisberg. It wouldn't be surprising if elements of that series were rolled into Ramon's character on The Flash.
THR also says that only two series regular (should the pilot go to series) roles remain to be filled following today's announcement that Iris West was also cast. Those will be Hartley Rathaway (The Pied Piper) and Harrison Wells, who appears to be a new character created for the TV series.
The rest of the cast as it exists will include Grant Gustin as Barry Allen/The Flash, Jesse L. Martin as Detective West, Rick Cosnett as Detective Eddie Thawne and Danielle Panabaker as Caitlin Snow. Thawne and Snow are also villains in the comics.
The Tony Award-winning musical is starting to provide quite a few key players to TV and film; Cristin Milioti, also from Once, had a career year in 2013 as she appeared in Martin Scorcese's The Wolf of Wall Street and won the coveted role of The Mother on CBS's long-running sitcom How I Met Your Mother, alongside Buffy the Vampire Slayer's Alyson Hannigan, Dr. Horrible's Sing-Along Blog star Neil Patrick Harris and Captain America: The Winter Soldier's Cobie Smulders.