Who invented Gurmukhi script?

Together with Guru Nanak, Bhai Lehna (1563–1606) who later came to be known as the second Guru of Sikhs, Guru Angad Dev, invented and perfected an alphabet and script called Gurmukhi. 

Guru Nanak wanted to serve the common people of Punjab by inventing a language for Sikh scripture that would be understood by them.

Bhai Lehna and the first Sikh Guru, Guru Nanak, invented the Gurmukhi script, the language of the Sri Guru Granth Saheb.

Hindu sacred writing was in Sanskrit, a language no one could read or understand. Gurmukhi, the language of the Sikh holy text, The Sri Guru Granth Sahib, means ‘from the mouth of the Guru.’

The word Gurmukh, a central concept in Sikhism, means ‘one whose face is turned towards the Guru.’

The opposite of gurmukh is manmukh, one whose face is turned towards his own small self, his ego. (As a relevant aside, the arch Guru in Sikhism is ‘God himself’ in ‘his’ role as instructor speaking to the soul of one who is attuned to that Voice.)

Bhai Lehna was tested again and again by Guru Nanak.
In serving Guru Nanak in every way, Bhai Lehna was serving the highest in himself.
That is what service is – ultimately a gift to yourself.

Bhai Lehna was like an arrow flowing in only one direction: towards his Guru, who reflected, like the moon, like all prophets and messiahs, the Guru of Gurus, God.

Into the Great Heart by Kamla K Kapur