Guru Har Rai Ji was the grandson of Guru Hargobind Sahib Ji and became Guru at fourteen. He kept the horse establishment his grandfather had raised, some two thousand two hundred, but fought nothing.
He maintained a dispensary at Kiratpur that treated anyone who came. The account most often told is that Dara Shikoh, Shah Jahan's eldest son, sent for a rare drug from that store and was given it without condition, and that when Dara later lost the war of succession to Aurangzeb and passed through the Punjab in flight, the Guru did not obstruct him.
Aurangzeb summoned him to Delhi over the matter. He sent his elder son Ram Rai instead. At the Mughal court Ram Rai altered a line of Guru Nanak Dev Ji's, changing musalman to beiman, to avoid offence. The Guru disowned him for it and never saw him again, and appointed his younger son Har Krishan, aged five, as successor.
Ram Rai was given land by the emperor and founded Dehradun. His line, the Ramraiyas, remained a separate sect.
The disowning of a son over one altered word is the sharpest statement in the whole tradition about the fixity of the text, and it is the reason the Guru Granth Sahib Ji is not edited.
He kept the armed retinue his grandfather had raised and used it in no campaign, which is the fact every account of him has to explain.
He is recorded as having kept gardens and a collection of medicinal plants at Kiratpur, which is what the dispensary drew on. It is the only botanical establishment attributed to any Guru.
He sent his elder son Ram Rai to Aurangzeb's court and disowned him for altering a line of scripture to please it. He passed the succession to his younger son, who was five.