Percival Graves was an exceptionally skilled wizard and an auror who worked for MACUSA. In the 1920s, Graves was tasked with tracking down whatever creature was terrorizing New York City. For some time, the suspicion fell on Newt Scamander and his escaped fantastic beasts (WFT).
Percival Graves was a descendant of Gondulphus Graves, one of the original twelve Aurors of MACUSA in early North America (Pm: MACUSA).
Other canon notes and references
In December, 1926, Graves was somehow replaced by Gellert Grindelwald, possibly using Polyjuice potion. When Grindelwald was finally captured, a spell revealed his true identity. The fate of the real Graves is unknown.
The real Percival Graves did exist, but we now know that the Graves we see on screen is an imposter, possibly as a result of the use of Polyjuice Potion. According to David Heyman:
SnitchSeeker: Is there a real Graves? what happened to him?
David Heyman: That's a very good question. I've been wondering ... I'm amazed more people haven't picked up on that. Yes, there was a real Graves. Yes, someone used some Polyjuice potion and took their place. I don't know where they are at the story's end, But yes, there was a real Graves. We didn't film him. We didn't film the Polyjuice. We just dived into the story midway through.
SnitchSeeker: Will we see Graves in the future?
Heyman: I doubt it.
SnitchSeeker: It is similar to what happened with Crouch and Moody in the fourth book?
SnitchSeeker: I guess Colin Farrell won't be back in the sequel?
Heyman: There's no plans to bring Colin back for the sequel.
A literal reading of the script suggests that the attack at the chateau in Europe happened the evening before Newt arrived in New York. This would mean that Grindelwald arrived in America just as Newt was arriving, which leaves little time for his attack on Graves.