Walker was a MACO soldier assigned to the Enterprise NX-01 during its mission in the Delphic Expanse in 2154.
During Enterprise's mission to destroy Sphere 41, Walker participated in the attempts to combat a group of Sphere Builders which had boarded the ship in an attempt to stop them. Walker contacted the bridge, informing the crew that they had secured main engineering. (ENT: "Zero Hour")
Walker was only heard over the intercom, voiced by an unknown actor.