Louis Donaldson

 Dr. Louis Donaldson  was presumably a member of the Black Mesa Science Team, involved in the research of creatures from Xen, prior to the Black Mesa Incident. During his work, he became the discoverer of the Barnacle creature, but unfortunately also its first victim. The Barnacle's full name, Cirripedia donaldsonia, was subsequently named after him.

Behind the Scenes

 * His name is likely a nod to Valve employee Louise Donaldson.