Mata Sundari ji was wife of Guru Gobind Singh (1666-1708), was the daughter of Bhai Ram Saran, a Kumarav Khatri of Bijvara, in present-day Hoshiarpur district of the Punjab. She was married to Guru Gobind Singh at Anandpur on 4 April 1684. On 26 January 1687, at Paonta, she gave birth to Sahibzada Ajit Singh, the eldest son of Guru Gobind Singh. Consequent upon the evacuation of Anandpur on the night of i6 December 1705, Mata Sundari, along with Mata Sahib Devan, was escorted by Bhai Mani Singh to Delhi. She rejoined Guru Gobind Singh in 1706 at Talvandi Sabo, where she heard the news of the martyrdom of her son and the other Sahibzadas as also of the death of her aged mother-in-law, Mata Gujari. She went back to stay at Delhi while Guru Gobind Singh left Talvandi Sabo for the South. At Delhi, Mata Sundari adopted a young boy whom she named Ajit Singh because of his resemblance to her own late son. After the passing away of Guru Gobind Singh at Nanded in October 1708, the Sikhs looked up to her for guidance. She appointed Bhai Mani Singh to manage the sacred shrines at Amritsar and also commissioned him to collect the writings of Guru Gobind Singh. She also issued under her own seal and authority hukamnamas to sangats. The hukamnamas since discovered and published bear dates between 12 October 1717 and 10 August 1730. Mata Sundari was disappointed in her adopted son, Ajit Singh. Emperor Bahadur Shah treated him as the successor of Guru Gobind Singh, called him to his court and gave him a robe of honour in September 1710. This went to his head and he started 1iving in style as a courtier. He grew arrogant and haughty even towards Mata Sundari who disowned him, and migrated to Mathura. Ajit Singh was later convicted for murder and was put to death on 18 January 1725. Mata Sundari returned to live in Delhi where she ,died in 1747. A memorial in her honour stands in the compound of Gurdwara Bala Sahib, New Delhi.
Encyclopedia of Sikhism edited by Harbans Singh ji.