Guru Nanak Dev ji, also called Guru Nanak [Dev being a respectful term for a godly person, and ji being another name denoting special respect], lived from 1469 to 1539, in the Indian subcontinent and was the founder of the Sikh religion. He was also the first of the ten Gurus or Spiritual leaders of the Sikh religion. Guru Nanak had the unique vision to create a new social and religious platform, in which all people would be treated fairly, with justice, eliminating all class discriminations. Though Sikhism has spiritual alignments with and respects other religions like Hinduism, Islam, etc. it is a distinctly separate spiritual practice based on the teachings of Guru Nanak.
Guru Nanak spent his life spreading the teaching of Sikhism into far and wide communities. The teachings of Guru Nanak were in the form of religious hymns, meant to be recited by the followers in their morning and evening prayers. All his hymns and teachings were collected by the second Guru, Guru Angad Singh, informally. But the more formal first compilation of the teachings was done by the fifth Guru, Guru Arjan Singh, into a holy scripture called the Adi Granth. This was later converted to the current, Guru Granth Sahib.
The first composition of Guru Nanak and his foremost and most significant teaching is called the Mool Mantar. Mool means basic or root and Mantar is a hymn to be repeated for spiritual practice. This is the beginning of the Guru Granth Sahib, and is also repeated several times. It describes the eternal reality and truth of the one and only God who exists, nameless, formless and transcendental. Jap ji Sahib is the next important composition of Guru Nanak and encompasses all the values and principles of Sikhism. It promotes good social behaviour, and worship of the one true God, with all our heart as the path to the divine within us. Guru Nanak is also attributed to the composition of some hymns called Sohila, which are a part of the daily worship of all Sikhs.
Guru Nanak, the first Guru and the founder of the Sikh religion, travelled across the Indian subcontinent to spread his unique vision of Sikhism.