McLellan was born in Casper, Wyoming, grew up in Orland, California, and fought in the Canadian Army in the Second World War.
Serving as a radio operator in the 12th Armoured Regiment (Three Rivers Regiment), RCAC, he met his wife Patricia Price in England during the war, and afterwards the couple settled in Pasadena, California, where McLellan attended the California Institute of Technology (Caltech).
The first one required someone to build a working electric motor that would fit inside a cube 1/64 inches (0.40 mm) on each side.
[3] The second challenge was for anyone who could find a way to inscribe a book page on a surface area 25,000 times smaller than its standard print (a scale at which the entire contents of the Encyclopædia Britannica could fit on the head of a pin).
McLellan appeared on television in relation to his achievement, and spent much of his career as an engineer in Caltech's Astronomy department, remaining a consultant there for the rest of his life.