Tanok was a Vulcan male and an ethnologist who lived on Earth for fifty years in the 22nd century.
Tanok once wrote a paper on Human physiology in which he suggested the Human race had reached a "plateau" in its evolution and would not advance further without genetic engineering. Knowing Humans would react violently to this, with the memory of Khan Noonien Singh and his "supermen" still a controversial topic, Tanok published his work in a privately circulated journal on Vulcan. Tanok privately believed Humans would come to see that the idea of genetic engineering was sound and also posed the question of whether or not Earth and the galaxy would have been a worse place if Khan had won the Eugenics Wars. Both Julian Bashir and Ezri Dax both knew of Tanok. (DS9 - Section 31 novel: Abyss)