Sikhism is based on the spiritual teachings of Guru Nanak, the first Guru (1469–1539), and the nine Sikh gurus that succeeded him. The Tenth Guru, Guru Gobind Singh, named the Sikh scripture Guru Granth Sahib as his successor, terminating the line of human Gurus and making the scripture the eternal, religious spiritual guide for Sikhs. Sikhism rejects claims that any particular religious tradition has a monopoly on Absolute Truth.
The Sikh scripture opens with Ik Onkar (ੴ), its Mul Mantar and fundamental prayer about One Supreme Being (God). Sikhism emphasizes simran (meditation on the words of the Guru Granth Sahib), that can be expressed musically through kirtan or internally through Nam Japo (repeat God's name) as a means to feel God's presence. It teaches followers to transform the "Five Thieves" (lust, rage, greed, attachment, and ego). Hand in hand, secular life is considered to be intertwined with the spiritual life. Guru Nanak taught that living an "active, creative, and practical life" of "truthfulness, fidelity, self-control and purity" is above the metaphysical truth, and that the ideal man is one who "establishes union with God, knows His Will, and carries out that Will". Guru Hargobind, the sixth Sikh Guru, established the political/temporal (Miri) and spiritual (Piri) realms to be mutually coexistent. Sikhism evolved in times of religious persecution. Two of the Sikh gurus – Guru Arjan (14 April 1563 – 25 May 1605) and Guru Tegh Bahadur (12 April 1621 – 19 December 1675), after they refused to convert to Islam, were tortured and executed by the Mughal rulers. The persecution of Sikhs triggered the founding of the Khalsa, as an order to protect the freedom of conscience and religion, with qualities of a "Sant-Sipāhī" – a saint-soldier.
The majority of Sikh scriptures were originally written in Gurmukhī alphabet, a script standardised by Guru Angad out of Laṇḍā scripts used in North India. Adherents of Sikhism are known as Sikhs, which means students or disciples of the Guru. The anglicised word 'Sikhism' is derived from the Punjabi verb Sikhi, with roots in Sikhana (to learn), and Sikhi connotes the "temporal path of learning".
Any human being who faithfully believes in
i. One Immortal Being,
ii. Ten Gurus, from Guru Nanak Sahib to Guru Gobind Singh Sahib,
iii. The Guru Granth Sahib,
iv. The utterances and teachings of the ten Gurus and
v. the baptism bequeathed by the tenth Guru, and who does not owe allegiance to any other religion, is a Sikh.
The basis of Sikhism lies in the teachings of Guru Nanak and his successors. Many sources call Sikhism a monotheistic religion, while others call it a monistic and panentheistic religion. According to Eleanor Nesbitt, English renderings of Sikhism as a monotheistic religion "tend misleadingly to reinforce a Semitic understanding of monotheism, rather than Guru Nanak's mystical awareness of the one that is expressed through the many. However, what is not in doubt is the emphasis on 'one'".