Tsar Bomba
The UR-500 was designed to be a very large ICBM, with the throw-weight necessary to deliver the 50-100 megaton Tsar Bomba like warhead. Under pressure from Khrushchev, the UR-500 was reworked as a space launcher, and eventually renamed the Proton, the latest version of which is still in service as of 2020.