Which Hindu god is not one of the 'Trimūrti', the triple deity of supreme divinity in Hinduism?

Krishna is not one of the Hindu gods of the 'Trimūrti', responsible for the creation, preservation and destruction of the world.

Krishna is a major deity in Hinduism. He is worshipped as the eighth avatar of Vishnu and also as the supreme God in his own right. He is the god of protection, compassion, tenderness, and love and is one of the most popular and widely revered among Indian divinities. Krishna's birthday is celebrated every year by Hindus on Krishna Janmashtami according to the lunisolar Hindu calendar, which falls in late August or early September of the Gregorian calendar.

'Trimūrti' or 'Trideva' is the triple deity of supreme divinity in Hinduism, in which the cosmic functions of creation, maintenance, and destruction are personified as a triad of deities, typically Brahma the creator, Vishnu the preserver, and Shiva the destroyer, though individual denominations may vary from that particular line-up. The legendary yogi Dattatreya is often treated as not only one of the 24 avatars of Vishnu, but also of Shiva and Brahma as well in a single three-headed body.