James Montgomery was a Union colonel that lead the raid on Combahee Ferry along with Harriet Tubman.
In the Timeless Universe
When the time team, consisting of Lucy Preston, Rufus Carlin, Wyatt Logan, and Garcia Flynn, first arrived to 1863, and saw how the Rittenhouse sleeper agent, Ryerson, used his knowledge of the future to stop what was a successful attack in the original timeline, they were spotted by Harriet Tubman. Wyatt explained to Tubman, dishonestly, that General George McClellan and Colonel James Montgomery sent them to help with the raid. Tubman went onto explain that Montgomery had all of his troops retreat after seeing how proficient the Confederates were, but that she would perform the raid with whatever men she had.
Later, to help Tubman's raid succeed, Lucy and Flynn ride to Port Royal to convince Colonel Montgomery to provide Tubman with troops. When they arrive, Montgomery is skeptical of the claim that the two, are Union spies, but Lucy goes on to explain that Montgomery needs to lend Tubman some troops so that she may recruit some of the 750 slaves she'll be able to free from the river plantations. Montgomery is skeptical of this claim as well, but seems to agree with Lucy, as he does end up providing Tubman with the necessary men.