Carl Gauss

Johann Carl Friedrich Gauss (30 April 1777 – 23 February 1855) was a German mathematician and scientist who contributed significantly to many fields. These fields include number theory, statistics, analysis, differential geometry, geodesy, geophysics, electrostatics, astronomy, and optics. He was sometimes referred to as the "Prince of Mathematicians" and called math the "queen of sciences." 
He was ranked as one of the most influential mathematicians.

At 24 years of age, he wrote a book called Disquisitines Arithmeticae, which is regarded today as one of the most influential books written in math. He also wrote the first modern book on number theory, and proved the law of quadratic reciprocity. In 1801, Gauss discovered and developed the method of least squares fitting, 10 years before Legendre, unfortunately, he didn't publish it. Gauss also proved that every number is the sum of at most three triangular numbers and developed the algebra of congruences.

Because of his great accomplishments, he was put on the German Ten Euro Bill.