Garrick, in comic book lore, was the original fastest man alive.
On the show, he will arrive in Central City to warn superhero Barry Allen/Flash (Grant Gustin) and his STAR Labs friends of an impending danger that he needs help to stop.
Garrick's appearance was teased in the finale, when his winged helmet flew through a wormhole into STAR Labs, said The Hollywood Reporter.
Also in the mix for the season is actress Shantel VanSanten as Patty Spivot, a more recent addition to the comics.
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The new season will pick up a few months later and there will be many new faces, executive producer Greg Berlanti revealed at Comic-Con.
Executive producer Andrew Kreisberg revealed Professor Zoom will be the big bad of the season.
He is faster than both Reverse-Flash and the Flash - and will be very difficult to catch. Wally West - another speedster from the comics - will also be joining the show.