Guardian

Gaurdians
The Gaurdians are a military(?) force of the remnants of the human race. Equipped with with guns and the ability to channel the Traveler's power, Gaurdians traverse the solar system and combat the malicious alien races that came to inhabit the solar system between the time that humanity was pushed back to Earth and when they began to take to the stars again. There are three known classes of Gaurdian: Hunters, Warlocks, and Titans. Hunters utilize stealth, Warlocks can use the power of the Traveler pretty much like magic, and Titans have "Mech Suits". It seems standard for them to own starships capable of interplanetary travel.

Trivia

 * They also appear to be known as knights.