Bhai Lehna was born in 1504 at Matte di Sarai in Ferozepur district, a Khatri trader and a devotee of Durga who led an annual pilgrimage to Jwalamukhi. He came to Kartarpur, stayed, and served Guru Nanak Dev Ji for six or seven years.
He was installed as the second Guru in 1539 and moved the centre to Khadur Sahib on the Beas.
Two things are attributed to him that shaped everything after. He gave the Gurmukhi script its settled form, standardising letters already in use among the traders and clerks of the Punjab so that the hymns could be written down in a script belonging to nobody else. And he collected the compositions of Guru Nanak Dev Ji, which became the basis of the volume Guru Arjan Dev Ji compiled sixty years later.
He established the langar at Khadur on a regular footing, with Mata Khivi Ji running it. She is named in the Guru Granth Sahib Ji by the bard Balwand, one of very few women named in it, for the langar she kept.
He also began the practice of physical training for the sangat, wrestling grounds at Khadur, which is the earliest thread of what became a martial tradition.
He passed the guruship to Amar Das, a man of seventy-three, again not to his sons.
Gurmukhi runs left to right, has thirty five letters in a fixed order, and takes its shapes from the Landa and Sharada hands already in use in the Punjab. What he did was settle the order, add the vowel signs the traders' shorthand left out, and fix the forms, which is what turns a shorthand into a script that can carry a text exactly.
He wrote sixty three shloks himself and they stand in the vars of the Guru Granth Sahib Ji signed as Nanak, following the convention that each Guru signed with the first one's name. That convention is why authorship in the volume is given by a number, mahalla one to mahalla nine, and not by a name.
He was named Angad, meaning of the body, by his predecessor. The succession outside the family was tested at once by Guru Nanak Sahib Ji's own sons and it held.