Short answers, pulled from the story.
Guru Arjan was the fifth of the ten Sikh Gurus, serving from 1581 until his death in 1606. He compiled the first official edition of the Sikh scripture, the Adi Granth, and is regarded as the first of two Sikh Gurus to be martyred. His death is considered a watershed event in Sikh history.
The Adi Granth was the first official edition of the Sikh scripture, compiled by Guru Arjan and completed on the 30th of August 1604. It included hymns from the first four Sikh Gurus, 2,218 hymns composed by Arjan himself, and contributions from 17 Hindu bards and 2 Muslim bards. It was installed in the Harmandir Sahib on the 1st of September 1604.
Jahangir ordered Arjan's arrest in 1606, accusing him of supporting a rebellion by his son Khusrau Mirza. According to Jahangir's own autobiography, the Tuzk-e-Jahangiri, Arjan's growing influence led Jahangir to conclude that if Arjan did not convert to Islam, the Sikh Panth had to be extinguished. Arjan refused to convert, to pay a fine of 200,000 rupees, or to alter the scripture, and died in Mughal custody.
Guru Arjan died in 1606 while in Mughal custody at Lahore Fort. Historical records and Sikh tradition are unclear as to whether he was executed by drowning in the Ravi river or died as a result of torture. Scholar J.S. Grewal notes that Sikh sources from the seventeenth and eighteenth centuries contain contradictory accounts of his death.
Amritsar is the city most closely associated with Guru Arjan. His father Guru Ram Das founded the settlement around a man-made pool, and Arjan completed the Gurdwara Harmandir Sahib temple complex there, installing the Adi Granth inside it in 1604. Amritsar is now the holiest pilgrimage site in Sikhism.
Guru Arjan composed 2,218 hymns, making his the largest single contribution to the Guru Granth Sahib. His work accounts for more than half the volume of the scripture. Scholars have described his compositions as combining spiritual depth with encyclopedic linguistic sophistication, drawing on Braj Bhasha forms and Sanskrit vocabulary.