Answer in Details
Shiva is called Mahadev because "Mahadev" means "Great God" or "God of Gods" (Maha = great, Dev = god) in Sanskrit. In Shaivism and many Hindu traditions, Lord Shiva is considered the Supreme Being, the ultimate reality (Paramatman), and the source from which all creation emanates.
Here are some reasons why Shiva is revered as Mahadev:
1.
Supremacy among Devas: Among the Trinity (Trimurti) of Hinduism—Brahma (the creator), Vishnu (the preserver), and Shiva (the destroyer and regenerator)—Shiva is often regarded as the highest, who transcends creation, preservation, and destruction.
2.
Source of All Divine Powers: Shiva embodies all aspects of existence: creation, preservation, and dissolution. As Mahadev, he is seen as the source from which all other gods derive their powers.
3.
Transcendence and Renunciation: Shiva is the epitome of asceticism and detachment (vairagya), teaching that ultimate reality is achieved by transcending desires and ego.
4.
Grace and Compassion: Shiva is known as Bholenath (the innocent lord), easily pleased and quick to grant boons to his devotees, regardless of their status or past.
5.
Scriptural References: Texts like the Shiva Purana, Linga Purana, and the Mahabharata refer to Shiva as Mahadev, emphasizing his unparalleled greatness.
In summary, Shiva is called Mahadev because he is revered as the supreme and most powerful deity, the lord of all gods, embodying both the destroyer and the benefactor, the ascetic and the householder, the compassionate and the fierce.