Uriah is the nickname of a Vortigaunt scientist who serves as Arne Magnusson's assistant at White Forest. There he grants access to the secondary silo to Gordon Freeman for him to cordon off the breach, then comes into the silo with Alyx when the breach is shut. Later on he assists Magnusson in teaching the ways of the Strider Buster to Freeman.
When the team first decided to make Vortigaunts ally characters for Half-Life 2, they played around with having a prominent Vortigaunt companion. Because of their bowed posture and semi-servile manner, this individual was dubbed "Heep", after the obsequious character Uriah Heep from Charles Dickens' novel David Copperfield. They finally included that prominent Vortigaunt in Episode Two, first known internally as "Labby", and when it became so popular among playtesters, he evolved into a fully developed character with a unique name (again reused from the name "Uriah Heep", but the first name this time), and a special place by Dr. Magnusson's side. Dickens' unused middle name for Uriah Heep will apparently be revealed in Episode Three (although Uriah Heep has no known middle name), suggesting another prominent Vortigaunt will be created.