It appears that Rip Hunter (Roger Darvill) will be assembling his merry band of time-traveling warriors to thwart the evil machinations of Vandal Savage. Savage definitely fits the criteria of "immortal threat" as described in the official synopsis for Legends of Tomorrow. What exactly Savage is up to in Legends of Tomorrow is still a mystery. And though immortal, Savage is typical depicted as the type of threat that usually wouldn't warrant the combined strength and abilities of Hunter, Atom (Bradon Routh), Firestorm (Victor Garber), Hawkgirl (Ciarra Renee), White Canary (Caity Lotz), Captain Cold (Wentworth Miller) and Heatwave (Dominic Purcell). My guess would be that Savage is not the only villain the LoT team will face and that Savage has his own evil squad providing support.
The actor that will be portraying Savage is also a big mystery. Perhaps one that will be unveiled at this year's SDCC?