Guru Nanak Dev, the founder of Sikhism, preached the unity of God and the equality of all people, rejecting caste discrimination and ritualistic practices. His teachings emphasized selfless service (seva), honest living (kirat karni), sharing with others (vand chhako), and spiritual devotion (naam japna). He advocated a life of humility, truth, and compassion. Guru Nanak’s philosophy inspired a reformist movement that emphasized social justice, harmony, and devotion. His teachings are immortalized in the Guru Granth Sahib, guiding millions of Sikhs worldwide.