Baba Dyal Singh founded the Nirankari movement at Rawalpindi around 1851, preaching a return to the formless, nirankar, and opposing idol worship and Brahminical rite in Sikh practice. He introduced the Anand marriage ceremony, which was later given statutory recognition in the Anand Marriage Act of 1909.
The original Nirankaris, now called the Sant Nirankari Mandal in one line and distinguished from them in another, moved to Chandigarh and Delhi after 1947.
A separate body, the Sant Nirankari Mission, developed in the twentieth century with a living guru, which put it in direct doctrinal conflict with orthodox Sikh position, since the Guru Granth Sahib Ji is the Guru and no living successor is accepted.
On Vaisakhi 1978 at Amritsar a Sikh protest march against a Nirankari convention ended in firing in which thirteen Sikhs were killed. That day is the point at which the Punjab conflict of the following decade is usually said to begin.
The distinction between the nineteenth-century reform movement and the twentieth-century mission is routinely collapsed in public discussion, and the confusion is not accidental.
The Anand ceremony is the part that lasted. Sikh marriages before it were performed with Brahmin priests and Vedic rite, and the reform put the couple's four circuits round the Guru Granth Sahib Ji with the Lavan of Guru Ram Das Ji in place of that. Nearly every Sikh marriage anywhere now follows a form assembled by a reformer at Rawalpindi.
He preached against the practice of his own community and not against anybody else's, which is what a reform movement is. He was driven out of Rawalpindi for it and set up at Dyalgarh, and the line he founded has stayed small, quiet and inside the fold ever since.
The two are constantly confused, including in reporting of the events of 1978, and the distinction matters to both of them.