He is the Supreme Being in Shaivism, one of the major traditions within Hinduism. Shiva is known as "The Destroyer" within the Trimurti, the Hindu trinity which also includes Brahma and Vishnu. In the Shaivite tradition, Shiva is the Supreme Lord who creates, protects and transforms the universe.
Lord Shiva is one of the most powerful God. He is Bholenath, an innocent compassionate God. And fierce Mahakal at the same time. He is not only considered as Adiyogi but he is also considered as the God of Gods. He is omnipotent, omniscient and omnipresent. In spite of him being considered as the destructor of life one has to understand that he is the reason for re-birth as well. He is the one who possesses both the generative and destructive powers of nature. Shiva is a very complex form who has control over both the macro and micro levels of the cosmic energy. Even in temples you will find a separate shrine for Shiva recognising him as the most powerful and fascinating deity of the Hindu trinity.
Theres a story back to a point when Shri Vishnu and Brahma fought among themselves as to who was the most powerful between them. As the Gods predicted disastrous results out of such a controversy, they requested Shiva to intervene and find a solution. Shiva then took the form of a lingam and asked them to travel in search of the aadhi which signifies “the beginning” and antham which signifies “the end” of the lingam.
Brahma flew upwards by transforming himself into a swan while Shri Vishnu travelled downwards by transforming himself into a boar. They remained unsuccessful in finding the beginning and end points of the lingam. Brahma finds a ketaki flower and requests it to tell a lie to Shiva about his victory over Vishnu in finding the beginning of the lingam. On doing so, Shiva appears from the centrally split part of the lingam and curses Brahma that he would not have any temples and people will never worship him. He passes the curse to the flower as well, by making it unsuitable and ineligible for worship.