Final answer:
Guru Gobind Singh Ji is the spiritual father of all Sikhs (Khalsas), having established the Khalsa in 1699 and provided structured guidance to the Sikh community.
Step-by-step explanation:
The spiritual father of all Sikhs (Khalsas) is Guru Gobind Singh Ji. He was the tenth Sikh Guru and established the Khalsa, a collective body of all initiated Sikhs, in 1699. Guru Gobind Singh Ji provided Sikhism with structured guidance and passed the Guruship to the Sri Guru Granth Sahib, the holy scripture of Sikhism, as the final and eternal Sikh Guru. While Guru Nanak Dev Ji was the founder of Sikhism, and other Gurus like Guru Arjan Dev Ji and Guru Tegh Bahadur Ji played significant roles in its development, it was Guru Gobind Singh Ji who formalized the Khalsa and is thus considered the spiritual father.