Diwan Mohkam Chand Nayyar was Hindu Punjabi Khatri. He is my great great great grandfather. My father & grandfather told me about his bravery and accomplishments. I was able to verify this ancestry lineage from Bahis in Haridwar being managed by our Kul-Purohit.
Anyone who believes in Shri Guru Granth Sahib's teachings is a Sikh ( a disciple/ student). Including myself, majority of Hindus in the world are also Sikhs as they believe in these teachings. They are not necessarily Singhs who should be wearing 5 Ks- Kanga (a comb), Kacha (cotton shorts worn under the clothes), Kara (a steel bracelet), Kesh (uncut hair), Kirpan (steel sword).
