Leonardo Fibonacci
The "greatest European mathematician of the middle ages" grew up with a North African education under the Moors and later traveled extensively around the Mediterranean coast. He would have met with many merchants and learned of their systems of doing arithmetic. He soon realized the many advantages of the "Hindu-Arabic" system over all the others.
He was one of the first people to introduce the Hindu-Arabic number system into Europe - the positional system we use today - based on ten digits with its decimal point and a symbol for zero:In other words, Fibonacci not only created the famed Fibonacci sequence, he also introduced the number system we use today!
Credit to: http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/fibBio.html