Dmitry Semionovitch Mirimanoff (Russian: Дми́трий Семёнович Мирима́нов, 13 September 1861, Pereslavl-Zalessky, Russia – 5 January 1945, Geneva, Switzerland) became a doctor of mathematical sciences in 1900, in Geneva, and taught at the universities of Geneva and Lausanne. Mirimanoff made notable contributions to axiomatic set theory and to number theory (relating specifically to Fermat's last theorem, on which he corresponded with Albert Einstein before the First World War). In 1917, he introduced, though not as explicitly as John von Neumann later, the cumulative hierarchy of sets and the notion of von Neumann ordinals; although he introduced a notion of regular (and well-founded set) he did not consider regularity as an axiom, but also explored what is now called non-well-founded set theory and had an emergent idea of what is now called bisimulation.
Mirimanoff became a member of the Moscow Mathematical Society in 1897.
Dmitry Semionovitch Mirimanoff (Russian: Дми́трий Семёнович Мирима́нов) was born in Pereslavl-Zalessky, Russia, on 13 September 1861. His parents were Semion Mirimanovitch Mirimanoff (Russian: Семён Мирима́нович Мирима́нов) and Maria Dmitrievna Rudakova (Russian: Мари́я Дми́триевна Рудакова). He was a great grandson of David A. (?) Mirimanian (later Mirimanoff) (Russian: Дави́д А. (?) Мириманян), a member of an old Armenian family settled in Georgia and an honorary citizen of Tiflis (now Tbilisi).