Prince Janusz Radziwiłł, also known as Janusz the Second or Janusz the Younger was a noble and magnate in the Polish–Lithuanian Commonwealth. Throughout his life he occupied a number of posts in the state administration, including that of Court Chamberlain of Lithuania, Field Hetman of Lithuania and Grand Hetman of Lithuania. He was also a voivode of Vilna Voivodeship, as well as a starost of Samogitia, Kamieniec, Kazimierz and Sejwy. He was a protector of the Protestant religion in Lithuania and sponsor of many Protestant schools and churches.