Sadhu Sundar Singh (Punjabi: ਸਾਧੂ ਸੁੰਦਰ ਸਿੰਘ, Urdu: سادھُو سُندر سنگھ; Hindi: साधु सुन्दर सिंह) (September 3, 1889 Patiala State, India) was an Indian Christian missionary. He is believed to have died in the foothills of the Himalayas in 1929.