Shani is one of the "Navagraha ”which are the nine primary celestial beings in Hindu astrology, or Jyotish. Shani is embodied in the planet Saturn. Shani is the Lord of Saturday; the word Shani also denotes the Seventh day or Saturday in most Indian languages.
The origin of word Shani comes from the following: Shanaye Kramati Sa: i.e. the one who moves slowly, as Saturn takes about 30 years to rotate around the Sun. Shani is also known as Shanaiscarya, Shani Bhagavan, Shaneesvara, Saneesvara, Shaneesvaran, Shani Deva.
Shani is a Deva and son of Surya (the Sun God) and his wife Chhaya (Shadow goddess) and hence also known as Chayyaputra. He is the cousin of Yama,the Hindu God of death. It is said that when he opened his eyes as a baby for the very first time, the sun went into an eclipse, which clearly denotes the impact of Shani on astrological charts. He is known as the greatest teacher. He is known in Hindu scriptures as the greatest trouble maker as well as the greatest well wisher. He is depicted dark in colour, clothed in black; holding a sword, arrows and two daggers and variously mounted on a black vulture or a raven.
The Story of Shani Dev
Once all the Nine Planets gathered together at one place and started talking to each other. Along with talking on many subjects the talk started on "Which planet was the most respectable among them?" They had arguments for long time, but to no avail. So they decided to go to Indra. So they all went to Indra. Indra was in a flux, he could not tell anybody lower or higher as he did not want to be victim of anybody's anger. After a while he said - "I am not very capable to decide this, but there is a king named Vikramaaditya now a days in Ujjayinee, who can tell you this." So, all the planets came to the king Vikram's court.