Even though Gorilla Grodd was responsible for bringing The Rogues together for the first time in the Silver Age, it makes more sense if Cold is the one who does it in The Flash, especially since he was the first super villain in the comics to deliberately target the Barry Allen iteration in the comics.
It’s hard to imagine bringing the Rogues to the big screen and not have Leonard Snart, a.k.a.
He’s one of Barry Allen’s oldest enemies, and depending on who you ask, he’s also his greatest adversary.
Not only is he skilled at assembling and reassembling his cold gun quickly, but he’s also an excellent strategist.