Albert Einstein renounced his German citizenship in 1896. At the time, he was a teenager from the Kingdom of Württemberg, a state within the German Empire, and he gave up that citizenship partly to avoid compulsory military service.
Einstein had moved to Switzerland in 1895 and wanted to build his future there. He later became a Swiss citizen in 1901, retaining Swiss citizenship for the rest of his life. His renunciation in 1896 therefore predates his scientific fame, the 1905 “miracle year,” and his Nobel Prize.
A common mix-up is 1933. That year, after Adolf Hitler came to power, Einstein formally surrendered his German passport again while in Belgium and chose not to return to Nazi Germany. He had regained German citizenship in 1914 when he moved to Berlin, so the question's 1896 answer refers to his first renunciation, not his later break with the Nazi regime.