According to the Sanathan Dharma (Hinduism) out of the three gods of the trinity, Lord Shiva is one of them. Lord Shiva is the destroyer but for the betterment of all. He has the third eye on his forehead which is said to destroy the universe, if opened. Lord Shiva who is also addressed as Natraja, (King of Dance), when angry can do the tandav nirtya, which means dance of destruction.
People pray to Lord Shiva for long life, good health. Devotees of Lord Shiva are confident that with his blessings even death can be turned away. And so Mritunjaya is one of Shiva`s names, which means one who is victorious over death.
Shiva is the most selfless one; during the samundra manthan (churning of sea) he chose to drink the pot of poison that came out of the sea. He stored the poison in his throat and hence was called Neelkanta (Blue throat).
For all Shiva devotees, Mahashivratri has a lot of significance. From morning onwards, devotees begin their fast and eat only fruits and some don`t even drink water for all twenty hours. The whole night of Mahashivratri is spent awake, singing devotional songs for Lord Shiva.
About Mahashivratri, it is told that on this day Shiva drank the pot of poison that came from the churning of sea (Samundra manthan). It was necessary that he stayed awake that night and the poison didn`t go below the throat. So to keep him awake the whole night, all gods started singing devotional songs praising Lord Shiva.