Kelso is the Enterprise-D transporter technician on duty when Data locks out the transporter to stop the exocomps being sent to their destruction in The Quality of Life.
Kelso appears in the sixth-season episode The Quality of Life. He operates the transporter during the crisis at the Tyrus VIIa mining station, where Jean-Luc Picard and Geordi La Forge are trapped by rising radiation.
William Riker's plan is to beam the small exocomp repair machines into the station's core and detonate them. Data, convinced that the exocomps are alive, refuses to allow it and disables the transporter controls from under Kelso's hands, leaving the technician unable to carry out the order.
The deadlock is broken when the exocomps are asked to choose for themselves; one of them stays behind so that the others and the officers can be recovered.