Jero was a performer, a member of a pre-warp civilization living on a Class-L planet in the Delta Quadrant. He worked for Kelis, who wrote their acting group's plays.

During the Voyager Eternals plays that they performed in 2376, he portrayed Tuvok, from the quiet and calm land of Vulcan, where there is no laughter, and no tears. He felt that that was impossible, and that the audience would either think Tuvok was an unfeeling monster, or that he was a bad actor if he didn't cry when Harry Kim and B'Elanna Torres were lost. He also played Kim, Chakotay and Tom Paris. (VOY: "Muse")

Jero was played by actor Michael Houston King.
His name comes from the script.