Aleksandr Lyapunov, Russian mathematician and physicist (b. 1857)
Aleksandr Mikhailovich Lyapunov (Russian: Алекса́ндр Миха́йлович Ляпуно́в, pronounced [ɐlʲɪkˈsandr mʲɪˈxajləvʲɪtɕ lʲɪpʊˈnof]; June 6 [O.S. May 25] 1857 – November 3, 1918) was a Russian mathematician, mechanician and physicist. His surname is variously romanized as Ljapunov, Liapunov, Liapounoff or Ljapunow. He was the son of astronomer Mikhail Lyapunov and the brother of pianist and composer Sergei Lyapunov.

Lyapunov is known for his development of the stability theory of a dynamical system, as well as for his many contributions to mathematical physics and probability theory.