Many legends are associated with the Sivaratri festival. According to one legend, Sivaratri is the wedding day of Lord Shiva and Parvati. As per another legend it is the night when Lord Shiva performed the Tandava Dance - the dance of primordial creation, preservation and destruction. Another legend associates Sivaratri with the great mythical churning of the ocean called Samudra Manthan. According to the legend, during the churning of the ocean, a pot of poison emerged. The gods and the demons were terrified as it could destroy the entire world. When they approached Lord Shiva for help, He, in order to protect the world, drank the deadly poison. However, he held it in his throat instead of swallowing it. This turned his throat blue. Since then Lord Shiva came to be known as ’Nilkantha’, the blue-throated one. Mahashivaratri celebrates this event by which Lord Shiva saved the world. Lord Shivs is considered to be unborn and hence cannot die. He is one without a beginning or an end and exists eternally.
Here is an interesting story about the birth & father of Lord Shiva :
When Lord Brahma presiding over Lord Shiva's marriage with goddess Parvati, asked Him, what his 'gotra is', Shiva at first remained silent. For the readers not familiar with Hinduism, Gotra is the lineage name started by first person that usually is an ancient Rishi sage in that family. For example, if someone's gotra is Kashyap, then he traces back his family lineage to the Kashyap Rishi. In some cases it may also mean the lineage of the family Guru.
So upon asking His lineage, Gotra by Brahma, Lord Shiva kept quite. Brahma asked again, but no reply came from Lord Shiva. So Brahma asked Shiva who is your father? Shiva said, you are my father Brahmaji. He again asked, who his grandfather is. Lord Shiva replied, it is Lord Vishnu. Lord Brahma asked again, so who is the father of Lord Vishnu? Shiva replied: it’s ME. And in that way, he revealed that he is the father of the universe and the cosmic manifestation. He is also the ParBrahm. Beyond Brahm. Lord Vishnu has worshipped Lord Shiva in his every incarnation. This is revealed by Lord Rama and Lord Krishna, who worshipped Lord Shiva, during their incarnation.
One may consider Vishnu and Shiva the two sides of the same coin, both are one only.
The origins of Shiva are unknown. He appears by his own energy. That is why he is also called Swayambhu.
As per the Hindu mythology, God is ONE. Lord Krishna is same as Lord Rama & also same as Lord Shiva. As per Bhagwat Gita Chapter Ten Verse - 23, God himself declares that He (Lord Krishna) is same as Lord Shiva.
"rudranam sankaras chasmi
vasunam pavakas chasmi
meruh sikharinam aham" (Bhagwat Gita: Chapter Ten verse 23)
"Sri Krishna said: Of all the Rudras I am Lord Shiva, of the Yakshas and Rakshasas I am the Lord of wealth [Kubera], of the Vasus I am fire [Agni], and of mountains I am Meru."
Now here below is a beautiful story which shows the kindness of Lord Shiva to his devotee & how He saved one of His devotee from the tiger.
Lord Shiva saves the Hunter:
Once a hunter was wandering in a dense forest, to chase a deer and suddenly he found himself on the banks of river Kolidum, where he heard the roar of a tiger. In order to defend himself from the tiger, he climbed up a tree close by. The Tiger sat on the ground below the tree without the purpose to leave.
The huntsman stayed at the tree whole night and to keep himself awake, he plucked one leaf after another from the tree and threw it down. There was a "Shiva Lingam" under the tree and gracefully the tree turned out to be a ''bilva'' tree (leaves of this tree are adored by Shiva). Without any knowledge, the huntsman had delighted the Lord Shiva by pouring Bilva leaves all night. With the arrival of the sun, the hunter looked down and found that the tiger has gone. In its place, Lord Shiva was standing there and he prostrated before the lord. With Shiva's blessings, he attained salvation from the bondage of the material world.
Om Namah Shivaye