What are Carl Friedrich Gauss accomplishments?

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 proved that every number is the sum of at most three triangular numbers and developed the algebra of congruences.