Jón Stefán Sveinsson, better known as "Nonni" (16 November 1857 in Möðruvellir in Hörgárdalur – 16 October 1944 in Cologne) was an Icelandic children's writer and member of the Society of Jesus.He left Iceland in 1870 for France, where he converted to Catholicism. His children's stories concerning a character named Nonni are well known in Iceland and parts of Europe. His childhood home in Akureyri is now a museum and he has featured on postage stamps. Jón Sveinsson's stories of growing up with his brother Ármann, nicknamed "Manni", were adapted into the television series Nonni and Manni.