Jalandharavatamurti is the form of Lord Shiva, as he destroyed the demon called Jalandhara. Lord Shiva has gained numerous titles by demolishing many demons in the history.
Lord Shiva is known for granting the boons to anyone who does severe penance towards him, irrespective of whether the devotee belongs to the demons or Gods. At the same time, as Lord Shiva is intolerant towards violence, dishonesty and wickedness, he ultimately supports the one who follows the Dharma.
Jalandhara, the demon who had obtained a lot many boons from Lord Shiva and Lord Brahma, misuses all of them to win over the Gods, Sages and other divines. His main objective is to capture all the corners of universe at all the times. He created an unending chaos and cared no one in the world. He also decided to capture the Satyaloka and Vykuntha. Those two places were conquered by him, as there was no force which can confront.
Out of his stupidity, he decided to win over Shiva. Knowing the fact that Jalandhara is coming to fight with him, Shiva wisely came up to Jalanadhara in disguise and objected him at the entrance of his abode Mount Kailash. He then placed a disc of fire and made Jalandhara stand in the middle of that, asking him to lift the disc. Lord Shiva, who is in the form of old man, said to Jalandhara that if he lifts up the disc, only then he would be eligible to fight with Shiva.
As the demon tried lifting the disc, the disc has cut the demon’s head into several pieces. Thus Lord Shiva has been entitled the name Jalandharavatamurti.