James Stewart Bain (19 December 1947 – 23 January 2016) was a Scottish musician, best known for playing bass guitar in the bands Rainbow and Dio. He also worked with Kate Bush and Thin Lizzy frontman Phil Lynott, co-writing on his solo albums.

On 23 January 2016, he died while in his cabin on Def Leppard's "Hysteria on the High Seas" cruise. He was due to perform on the cruise with his group Last In Line the following day. The performance did not go ahead, and band members informed fans on the cruise that he had been battling pneumonia for some time. The cause of death was determined to be lung cancer tho he had not been diagnosed with cancer and was aware only of his pneumonia. He is interred in Forest Lawn Memorial Park (Hollywood Hills), not far from his bandmate Ronnie James Dio.