The creator of this ageless logo is sadly unknown, but one can imagine him or her toiling over a set square and compass to produce this glorious design.
The roundel––in earlier years known as the 'bulls-eye' or 'target'--was first used in the 19th-century as the symbol of the London General Omnibus Company: a wheel with a bar across the center bearing the word 'General.'
Its usage on the Underground stems from the decision in 1908 to find a more obvious way of highlighting station names on platforms. The red circle with blue name bar was quickly adopted with the word "Underground" across the bar.
Mind the gap!