Since speedsters — especially The Flash and Reverse-Flash — are always tinkering with the timeline, there is a seemingly endless supply of alternate Earths, and the Legends are constantly time-traveling (to the past and the future) in The CW's DC Universe, it can be hard to keep track of which version of which character is being shown.
With Reverse-Flash, it is especially difficult since Eobard Thawne (Matt Letscher) was erased from existence in the first season finale of The Flash, but an earlier version of him — before he killed Harrison Wells and got stuck in the past — survived because, according to Executive Producer Andrew Kreisberg, an interesting aspect "of time travel is that time doesn’t unfold linearly."
In the midseason finale of DC's Legends of Tomorrow, there was an interesting moment when Dr. Martin Stein (Victor Garber) encounters Thawne and asks him if they know each other. Thawne replies, "Let's just say, it's complicated." So, which version of Thawne was that?
This is not a Reverse-Flash from a different Earth if that’s what you mean — after all, Eobard seemed to know who Stein was during the winter finale. “We are going to find out shortly on Legends of Tomorrow just how this Eobard links into the Eobard from The Flash,” Matt Letscher says, “where he’s coming from, and more importantly, where he’s going to after this.” - EW
MORE: Legends of Tomorrow Star Victor Garber On the Show's Evolution, Musical Possibilities, And More / Legends of Tomorrow's Victor Garber Never Wants To Go Back to the Titanic: "That's a Sacred Territory" / Legends Of Tomorrow: Camelot 3000 Photo Shows A Bloody Battle Scene / DC's Legends of Tomorrow Concept Art of Citizen Steel / Photos: The Legends of Tomorrow Travel To the '20s To Battle the Legion of Doom in "The Chicago Way"
Based on the characters from DC Comics, DC's Legends of Tomorrow is from Bonanza Productions Inc. in association with Berlanti Productions and Warner Bros. Television, with executive producers Greg Berlanti (Arrow, The Flash, Supergirl), Marc Guggenheim (Arrow, Eli Stone, Percy Jackson: Sea of Monsters), Andrew Kreisberg (Arrow, The Flash, Eli Stone, Warehouse 13), Phil Klemmer (The Tomorrow People, Chuck), Chris Fedak (Forever, Chuck), and Sarah Schechter (Arrow, The Flash).
Keep in mind: Beginning January 24, 2017, DC's Legends of Tomorrow will be moving from Thursdays at 8pm to Tuesdays at 9pm following The Flash.