Carl Friedrich Gauss wrote a beautiful textbook in Latin for (Algebraic) Number Theory titled “Disquisitiones Arithmeticae” (when he was 21 years old). In 21st century, Manjul Bhargava is extending and simplifying the ideas of Gauss. His PhD thesis (at age of 26 years) generalized Gauss’s classical law for composition of binary quadratic forms to many other situations. For a glimpse of his work, refer his article: The Factorial Function and Generalizations
Like other great mathematicians, he lives mathematics, for example read: Numbers, toys and music: A conversation with Manjul Bhargava
Last year (at age of 40 years) he was awarded the most prestigious award on our planet for young mathematicians, “Fields Medal” for :
developing powerful new methods in the geometry of numbers, which he applied to count rings of small rank and to bound the average rank of elliptic curves.
You can read his beautiful lecture on his contributions to mathematics at: Answers on a donut – the Fields medal lecture of Manjul Bhargava