Lord Bhairava is described as a Raudra Rupa, i.e., fierce form of Lord Shiva. In Hinduism, eight distinct forms of Lord Bhairava are worshipped collectively known as the Ashta Bhairava. Kalabhairava is one among these eight forms. In the Brahmavaivarta Purana, the eight Bhairavas are named Mahabhairava, Samhara Bhairava, Asitanga Bhairava, Rudra Bhairava, Kalabhairava, Krodha Bhairava, Tamrachuda Bhairava and Chandrachuda Bhairava.
This form of Lord Shiva as Kalabhairava is regarded as the presiding deity of time and death. The word Bhairava means 'the terrifying and destructive one' or 'the remover of fear.' Worship of Lord Kalabhairava destroys all known and unknown fears residing in the mind and grants victory over enemies. Kalabhairava is also worshipped for protection from evil spirits such as ghosts, spirits and malevolent entities.

Generally, nighttime is considered most suitable for His worship. Most devotees worship Him on Sunday, Tuesday and Saturday. The Krishna Paksha Ashtami of every month is observed as Masika Kalashtami and Kalabhairava Jayanti is celebrated on the Krishna Paksha Ashtami of the month of Margashirsha.
According to the scriptures, the legendary account of the origin of Lord Kalabhairava is as follows.
Nandishvara said - "O Sanatkumara Ji! Bhairava is the complete incarnation of Supreme Lord Shiva. Once, Lord Brahma was seated on Mount Sumeru. At that time, all the Gods assembled there and bowing to Brahma, asked - 'O Prajapati! What is the imperishable element of creation? Kindly enlighten us about the ultimate truth of existence.' Under the influence of Lord Shankara's illusion, Brahma, though unaware of the imperishable truth, began to describe it and said - 'O sages! I shall describe the true nature of the imperishable element, listen carefully. There is no deity greater than me. I alone am the creator of this universe, self-born, unborn, eternal enjoyer Brahma. I alone initiate and withdraw creation. There is none superior to me in the entire universe.'
Among those sages, Lord Vishnu was also present. Hearing Brahma's self-glorifying words, Vishnu said - 'O Brahma! What kind of conduct is this? You should remember well that it is by my command that you were established as the creator of the universe.'
Thus, a debate began between Lord Vishnu and Lord Brahma to establish their respective superiority and both started citing Vedic statements in support of their claims. At that moment, the four Vedas appeared in embodied form before them. First, the Rigveda said - 'He in whom all beings exist, from whom all creation proceeds and who is known as the Supreme Principle, He alone is Rudra.' Then the Yajurveda said - 'He through whom our authority is established, who is worshipped through various sacrifices and Yogic practices, the omniscient and all-seeing, He alone is Lord Shiva.' Thereafter, the Samaveda said - 'He who deludes the entire world, whom Yogis seek, by whose radiance the universe is illuminated, He is none other than the three-eyed Shiva.' Finally, the Atharvaveda said - 'He who can be realized only through unwavering devotion, who is free from all suffering, He alone is the Supreme Lord Shiva.'
Hearing these words of the Vedas, Lord Vishnu and Brahma Ji said - 'O Vedas! This is merely your ignorance. How can Shiva who dwells constantly with Shiva, remains unclothed, is yellowish in complexion and is smeared with ash and dust be considered the Supreme Principle?'
Hearing this, the all-pervading Omkara declared - 'Lord Shiva is the bearer of Shakti. Without His power, He cannot act. Though He engages in divine play, undoubtedly, He alone is the Supreme Lord.'
Even these words did not satisfy Brahma and Vishnu and their dispute continued. Suddenly, between them appeared a tremendously fierce and radiant column of light, i.e., Prakasha Punja, with neither beginning nor end. Its brilliance began to burn Brahma's fifth head. Immediately, the trident-bearing, blue-red-hued Lord Shiva appeared. Brahma Ji said to Him - 'O Neela Lohita, Chandramauli! Don't frighten me. I know you well. In ancient times, you were born from my head and because you cried, I named you Rudra. O son, take refuge in me; I shall surely protect you.'
Hearing these arrogant words, Lord Shiva became enraged and ready for dissolution. From His intense wrath emerged a being named Bhairava. Lord Shiva commanded him - 'O Bhairava! Discipline Brahma and uphold creation. You are like Time itself; therefore, you shall be worshipped as Kalabhairava. O Lord of Time! Among all sacred cities, Kashipuri is supreme. I appoint you as its eternal guardian. You shall record all sinners who dwell there.' Upon receiving this boon, Kalabhairava severed Brahma's fifth head with the nail of His left-hand finger. Distressed by His condition, Brahma began reciting the Shatarudriya. Vishnu and Brahma realized the truth and accepted Lord Shiva as Parabrahma Paramatma, i.e., the Supreme Absolute. When their arrogance was destroyed, Lord Shiva granted them fearlessness.
Thereafter, Lord Shiva instructed to Kalabhairava - 'O Neela Lohita! Honor Brahma and Vishnu and roam as a mendicant bearing Brahma's skull to absolve the sin of Brahma Hatya.' Lord Shiva then manifested a maiden named Brahma Hatya. Lord Shiva said to Kalabhairava - 'Go to Kashi before this maiden arrives there and direct her to wander in any place other than Varanasi. After wandering in all places, this maiden will return to Kashi, after which she will attain liberation.' Since then, by Lord Shiva's command, Kalabhairava resides in Kashi and hence He is known as the Kotwal of Kashi."
Thus, Lord Shiva manifested as Kalabhairava to destroy the arrogance of Brahma and Vishnu, impart knowledge of the Supreme Truth and resolve their dispute of superiority.
Kalabhairava is described as extremely terrifying and fearsome. He is dark and bluish in complexion, with eyes blazing with the fire of wrath. His head is adorned with matted locks. He wears Gajacharma or Baghambara, i.e., elephant hide or tiger skin, though in some depictions He is shown nude. Serpents adorn His body as sacred thread and waist-belt, and He wears Munda Mala, i.e., a garland of skulls around His neck. He is usually depicted as four-armed, holding a trident, noose, staff and axe. His vehicle is a dog, symbolizing Maya, i.e., the great illusion.
Lord Kalabhairava is a self-manifested incarnation of Lord Shiva; hence, no separate family is described. Goddess Parvati is Lord Shiva's consort. Lord Ganesha and Lord Kartikeya are His sons.
Moola Mantra -
ॐ कालभैरवाय नमः।
Om Kalabhairavaya Namah।
Beeja Mantra -
ॐ ह्रां ह्रीं ह्रौं काल भैरवाय नमः।
Om Hraam Hreem Hraum Kala Bhairavaya Namah।
Kalabhairava Gayatri Mantra -
ॐ कालाकालाय विद्महे कालातीताय धीमहि।
तन्नो काल भैरव प्रचोदयात्॥
Om Kalakalaya Vidmahe Kalatitaya Dhimahi।
Tanno Kala Bhairava Prachodayat॥