Duke wanders the Commonwealth in his suit of power armor, searching for parts the Atom Cats can use to build and maintain their power armor suits. He can be found via a random encounter in various locations, scrounging for parts in destroyed cars and will provide the Sole Survivor with directions to the Atom Cats garage in their Pip-Boy. He is also seen acting as the gate guard at the Atom Cats garage.
Duke is flagged as protected and will only be knocked down temporarily upon being mortally wounded by a hostile NPC.
However, Duke can be killed by NPCs while defending the garage from Gunners.
Despite his above-average health and suit of power armor, Duke is armed only with a low-tier rifle (up to combat rifle / assault rifle) and is only average in a fight, especially against tougher enemies such as super mutants or higher-level raiders or Gunners.
If you follow Duke after interacting with him during a random encounter, he will walk back to the Atom Cats garage.