Charles Babbage developed the first plans for the difference engine in 1821:
Babbage developed two mechanical calculators, the difference engine and the analytical engine. During his lifetime he could, however, not build a functional engine but the latter served as the predecessor of the modern computer. His interests and activities reach far beyond pioneering work in this field.
(Source: http://de.wikipedia.org/wiki/Charles_Babbage#Wissenschaftliches_Werk)
More details on Charles Babbage
