Blaise Pascal

Leibniz is best known for the co-invention of calculus along with Newton and the acrimonious rows that ensued between them.

However, for hardware enthusiasts an even more significant contribution was his introduction of the multiplier wheel into the Pascaline, an adding machine invented in 1642 by Blaise Pascal..

Source: http://www.i-programmer.info/news/82-heritage/2682-father-of-calculus-and-calculators-born-365-years-ago-today.html