Future Guy is associated with one of the factions in the Temporal Cold War. The name originated with fans, but it fit so well that B&B started referring to the character by the nickname in scripts and interviews.
Future Guy is an utterly undeveloped character. B&B freely admitted that they never determined his true identity or developed any backstory for him. In this way, he is symbolic of the lack of thought and effort that went into the writing of Star Trek: Enterprise.