Lord Narasimha is the fourth incarnation of Lord Maha Vishnu who incarnated to kill Demon Hiranyakashyap and to save his devotee Prahlada. According to Bhagavata Purana Lord Maha Vishnu in his avatar as Varaha killed Demon Hiranyaksha. The Demon Hiranyakshas brother Hiranyakashipu angered by this gained mystical powers from Brahma by undergoing many years of austerity and penance so that he could take revenge on Vishnu. Pleased by this Lord Brahma gives him the boon that Hiranyakashipu could not be killed by human, God or animal or during the day or night or on the threshold of a courtyard or on the earth or space or using any weapon.  So after getting a boon Hiranyakashyap returned to his kingdom and began to trouble the Gods. He also declared himself as God and ordered all to worship him. When his son Prahlada told him that Vishnu is the only God and cannot accept his father as God he tried to kill Prahlada. The servants threw Prahlada from top of mountains and in to the sea but could not kill him. Snakes and fire also could not harm him. 

The Demon asked Prahlada that is Vishnu present in this pillar and took his mace to hit the pillar. Lord Vishnu emerged from the pillar in his incarnation as Lord Narasimha with the head of a Lion and body of the man. The Demon King hit Narasimha with his mace but Narasimha brushed it aside swiftly. It was twilight and Narasimha caught hold of the demon Hiranyakashipu. He sat on the threshold of the court room, placed the body of the demon on his thighs, and pierced his nails into the body of the demon and broke open his stomach killing him.

It is believed that Lord Narasimha protects his followers when they are in extreme danger. He also saved Adi Sankara from being sacrificed to the goddess Kali by a Kapalika. As a gesture of gratitude Adi Sankara composed the Laksmi -Narasimha stotra in praise to Lord Narasimha.

Lord Narsimha is recognized in the scriptures by a variety of forms. He is said to have more than 74 forms on the basis of his different postures or weapons. Out of this 9 forms are the most popular. The most popular out of the nine is his Lakshmi Narasimha form. The nine forms of Narasimha (Nava Narasimha) are

1. Ugra Narasimha

2. Krodha Narasimha

3. Malola Narasimha

4. Jwala Narasimha

5. Varaha Narasimha

6. Bhargava Narasimha

7. Karanja Narasimha

8. Yoga Narasimha

9. Lakshmi Narasimha

Narasimha Bija mantra

Om Kshraum

Chanting this Bija Mantra is said to removes all sorrows and fears.

Narasimha Maha Mantra

The Mantra:

Om Hrim Ksraum ugram viram maha-vishnum
jvalantam sarvato mukham
nrisimham bhishanam bhadram
mrityur mrityum namamy aham

Meaning:

"I bow down to Lord Narasimha who is ferocious and heroic like Lord Vishnu. He is burning from every side. He is terrific, auspicious and the death of death personified."

Narasimha Gayatri Mantra

Mantra:

Om Vajranakhaya Vidmahe
Tiksnadamstraya Dhimahi
Tanno Narasimhah Pracodayat

Meaning:

Om let us meditate the half-man and half-lion form of the Lord Narasimha. May this great God with his nails pierce our ignorance and with his fierce sharp-tooth destroy the demon of darkness and illuminate our mind and understanding.