Nonarithmetic superrigid groups: Counterexamples to Platonov's   conjecture
  Margulis showed that "most" arithmetic groups are superrigid. Platonov conjectured, conversely, that finitely generated linear groups which are superrigid must be of "arithmetic type." We construct counterexamples to Platonov's Conjecture. 
Hyman Bass, Alexander Lubotzky