Explanation:

 Guru Arjan (15 April 1563 – 30 May 1606) was the first of the two Gurus martyred in the Sikh faith and the fifth of the ten total Sikh Gurus. He compiled the first official edition of the Sikh scripture called the Adi Granth, which later expanded into the Guru Granth Sahib.
Guru Hargobind (19 June 1595 - 3 March 1644), revered as the sixth Nanak, was the sixth of ten Gurus of the Sikh religion. He had become Guru at the young age of eleven, after the execution of his father, Guru Arjan, by the Mughal emperor Jahangir.
Guru Har Rai (16 January 1630 – 6 October 1661) revered as the seventh Nanak, was the seventh of ten Gurus of the Sikh religion.He became the Sikh leader at age 14, on 8 March 1644, after the death of his grandfather and sixth Sikh leader Guru Hargobind.He guided the Sikhs for about seventeen years, till his death at age 31.
Guru Har Krishan (7 July 1656 – 30 March 1664) revered as the eighth Nanak, was the eighth of ten Gurus of the Sikh religion. He became the youngest Guru in Sikhism At the age of five, on 7 October 1661,succeeding his father, Guru Har Rai.He contracted smallpox and died of the disease in 1664 before reaching his eighth birthday.