Austin Roe was an American spy during the American Revolution and part of the Culper Ring, a spy network.
In the Timeless Universe
In the original timeline, Austin Roe was a part of the Culper Ring and worked for General George Washington, though they never met face-to-face.
In the altered timeline, Garcia Flynn takes advantage of the two never meeting by killing Roe and then pretending to be him. While pretending to be Roe, Flynn warns about Benedict Arnold's betrayal and convinces him that Lucy Preston, Wyatt Logan, and Rufus Carlin are also spies part of the Culper Ring. Washington puts the four on a mission to go into British territory and capture Arnold.
Austin Roe at Wikipedia
Culper Ring at Wikipedia