Ik Onkar is the opening of Sikh scripture, and its most important word is written not as a name but as a numeral: the figure one, followed by the sign for onkar, the primal sound and being. The Sikh tradition makes a deliberate point of this. By stating oneness in a character that cannot be declined, pluralised or turned into a proper name, the Mul Mantar that opens the Guru Granth Sahib asserts a single, formless, uncreated reality in a way that resists the multiplication of gods and even the fixing of a name.
The phrase heads the fuller creedal statement that follows, true name, creator, without fear, without enmity, timeless, unborn, self-existent, which Guru Nanak set at the very front of the scripture and which Sikhs recite daily. Onkar echoes the Indian Om while the prefixed numeral pulls it firmly toward an uncompromising monotheism, and the combination captures something characteristic of early Sikh teaching: that it drew on the religious vocabulary around it while insisting, at the first word, on a oneness it would not let that vocabulary dissolve.