Colossus was the world's first programmable electronic digital computer. It was designed by research telephone engineer Tommy Flowers to a brief by the senior staff at the Government Code and Cypher School (GC&CS) at Bletchley Park during World War Two.

Pioneering work by the now-famous Alan Turing contributed to the design but credit needs to go to the largely-unknown Mr Flowers for implementing the design of the computer and constructing it. It went on to make great contributions to the war effort by enabling top-level German/Nazi radio messages to be decoded.