Sikhs affirm Ik Onkar, One, the opening words of the Guru Granth Sahib and of the Mul Mantar, the foundational creed traditionally composed by Guru Nanak, the faith's first Guru, in the late fifteenth or early sixteenth century. It proclaims a single, formless, eternal creator God, without birth or death, self-existent, beyond fear and enmity, realized by grace through the Guru. The Mul Mantar goes on to describe this God with a string of further attributes, commonly rendered as Truth is the Name, Creator, without fear, without hatred, timeless in form, unborn, self-existent, known by the Guru's grace, a formula repeated at the head of most sections of the scripture and treated as a summary creed of the entire faith. The one God is beyond gender and image and is not incarnate; the divine is known not through idols or avatars but through meditation on the Name (Naam) and through the teaching of the Gurus enshrined in scripture.
Guru Nanak's teaching of divine oneness developed in explicit tension with both the caste-structured ritualism he observed in the Hindu society around him and the exclusivist claims he encountered in Islam, and it grounded the practical institutions, such as the shared community kitchen (langar) open to all regardless of caste or creed, through which Sikh belief in one formless God for all people was given concrete social form from the movement's earliest years.