Slab

Slabs were robotic beings used as basic slave drones that resembled motorcycle couriers. They were solid leather throughout their whole body and always travelled in pairs.

Two such Slabs were henchmen of Florence Finnegan while she hid from the Judoon. The Tenth Doctor killed one with an X-ray with radiation increased by 5000%, while the other was destroyed by a Judoon blaster. (TV: Smith and Jones)

Slabs worked for Uvlavad Kudlak and were helping him to capture children for the war of the Uvodni against the Malakh Empire. (TV: Warriors of Kudlak)

When Amélie Plasmavore disguised herself as a human child, she had two Slabs act as her parents, Henri Plasmavore and Madeleine Plasmavore. (PROSE: Christmas with the Plasmavores)

Behind the scenes
According to Doctor Who: The Encyclopedia, Mat Dorman and Michael Williams portrayed the Slabs in Smith and Jones.