According to a popular legend, Lord Hanuman was born on a full moon day and his father Kesari was the son of Lord Brihaspati. His mother Anjana was a celestial body (Apsara) who got cursed by a sage to live on earth. She was redeemed from her curse only after doing 12 long years worship of Lord Shiva, and by giving birth to Lord Hanuman.
Thus, Hanuman is regarded as an incarnation or reflection of Lord Shiva (11th Rudra avatar).
The Holy epic, Ram Charita Manas written by Goswami Tulsi Das, beautifully narrates the role of Vayu dev (God of wind) in Hanuman’s birth. The epic describes that Vayu God played an important role to transfer Lord Shiva’s energy to Anjana’s (Mother of Hanuman) womb. Thus, Lord Hanuman is often called Vayuputra, which means the son of Vayu.
On the auspicious day of Hanuman Jayanti, devotees love to remember lord Hanuman as a naughty character in his childhood days. One such legend beautifully explains that lord Hanuman crossed several mountains and flew to great heights to eat the Sun, thinking it as a ripe fruit.
A baleful planet, Rahu which was on its way to form an eclipse with the Sun, came in front of the little Hanuman and stopped Him midway. Hanuman easily defeated Rahu (who later requested Indra, the king of heaven, for assistance). To this, Indra responded immediately and threw His powerful weapon Vajra (thunderbolt) and hit the young Hanuman and made Him unconscious.
After this event, God Vayu found his son lying in an unconscious state on earth, and an angry Vayu made life difficult for all living beings on the planet. Later,
Lord Indra and all demigods realized that they made a huge mistake and revived the young Hanuman and blessed Him with several boons.