25. Semion Mogilevich
We are continuing our list of worst, most feared, biggest gangsters in the world with Semion Mogilevich who is believed to be the boss over all bosses of the Russian mafia. In his long career of being a criminal, he was accused of many crimes such as drug trafficking, hiring killers, and smuggling gems. Anonymous sources also revealed that he tried to sell nuclear material to Al-Qaeda.