Ralph Adebayo was a crewmember on the Moonbase. He was a geologist and acted as a general handyman.
He was working in the food stores with Ben and noticed that some of the food sacks had holes in them. When he sent Ben on an errand, he was abducted and partially converted by the Telosian Cybermen and used by them to work the Gravitron controls. (TV: The Moonbase)
Behind the scenes
While credited only as "Ralph", in some photos the surname "Adebayo" can be seen on his uniform.
Ralph has a tricolour flag on his uniform. In surviving photos, the coloured stripes on the flag are the same colour which would indicate it's the Nigerian flag (two green and one white), fitting his surname.