Explanation:

- Guru Gobind Singh was the tenth Sikh Guru.

- He was born in 1666 and became the Guru in 1675, leading the Sikhs through significant religious and military efforts.

- Guru Gobind Singh founded the Khalsa in 1699, formalizing a community of committed Sikhs.

- His contributions were pivotal in shaping the spiritual and martial ethos of Sikhism.

- Option 2: Ninth - This was Guru Teg Bahadur, the father of Guru Gobind Singh.

- Option 3: Fifth - This was Guru Arjan Dev, known for compiling the Adi Granth.

- Option 4: Eighth - This was Guru Har Krishan, remembered for his wisdom and compassion at a young age.