In the Hindu pantheon, Shiva is the "Auspicious One," a major deity. He is the Destroyer, as Brahma is the Creator and Vishnu is the Preserver. Together, these deities are the trimurti, or the Hindu trinity.
Shiva is also associated with time, the destroyer of everything. In his good aspect, Shiva represents benevolence and goodness; he is a protector. He is also a destroyer, but his destruction is positive, leaving a clean slate for something new and fresh to be created.
Shiva's main task in the pantheon is the destruction of the universe at the end of each Hindu cycle of time. He also protects the sacred Hindu texts, the Vedas, and is the patron of Yogis and Brahmins.