G. Freiman is a mathematician known for his contributions to the field of combinatorial number theory. His work often focuses on additive number theory, which studies how numbers can be combined to form sums and the properties of these sums. Freiman is particularly recognized for the Freiman's theorem, which provides insights into the structure of sets of integers with small sumsets. This theorem has implications in various areas of mathematics, including combinatorics and additive combinatorics, and has influenced further research in these fields.