Theodosius Dobzhansky was a prominent geneticist and evolutionary biologist, born in 1900 in Ukraine. He is best known for his work on the role of genetics in evolution, particularly through his research on Drosophila fruit flies. Dobzhansky's famous phrase, "Nothing in biology makes sense except in the light of evolution," highlights his belief in the importance of evolutionary theory in understanding biological processes. Dobzhansky played a key role in the development of the modern synthesis, which integrated genetics with Darwinian evolution. He contributed significantly to the understanding of speciation and the genetic basis of adaptation. His work laid the foundation for many concepts in evolutionary biology and influenced future research in the field.