Sir John Spencer Login (9 November 1809 – 18 October 1863) was a Scottish surgeon in British India, best remembered as the guardian of Maharajah Duleep Singh and the Koh-i-Noor diamond following the annexation of Punjab and Last Treaty of Lahore. It was under Login and his wife's guidance that Duleep Singh converted to Christianity and was escorted to England in 1854. After a final trip to India, Login died shortly after his return to England in 1863.