Brahman—God the Absolute—creates the world, sustains it and withdraws it back into Himself (vide Brahmasūtras 1.1.2). In paurāṇic Hinduism this Brahman is described as three deities: Brahmā responsible for creation; Viṣṇu responsible for its sustenance; and, Rudra or Śiva responsible for its destruction at the end of a cosmic cycle. These three deities correspond to the three guṇas (rajas, sattva and tamas) in the cosmic play of creation, sustenance and destruction.
They are the Trimūrtis (or the Hindu Trinity).
There are composite images in which all the three gods are represented, like Dattātreya.