Gilbert is a green, filthy alien -- the one you see at your right on the screen!
He was a character featured in a TV show called "Get Fresh", where he was one of the co-hosts, presenting cartoons in the mornings.
The show aired from 1986 through 1988 - Then he was on "Gilbert's Fridge" (1989), "Gilbert's Late" (1990) and "An Afternoon on the Moon" (1994).
"Gilbert Escape from Drill" was created by "Enigma Variations", and publishd by "Again Again" in 1989 for the Spectrum. The MSX version was released on the same year.