Ajit Singh (11 January 1687 – 7 December 1705), also referred to with honorifics as Sahibzada Ajit Singh or Baba Ajit Singh, was the eldest son of Guru Gobind Singh. His younger brothers were Sahibzada Jujhar Singh, Sahibzada Zorawar Singh and Sahibzada Fateh Singh. He was killed during the Second Battle of Chamkaur.
Baba Ajit Singh Ji was born to Mata Sundari Ji and Guru Gobind Singh Ji at Paonta Sahib on 26 January 1687. He was brought up in Anandpur, where his education included religious texts, history and philosophy. He received training from Baba Jeevan SinghJi (Bhai Jaita Ji) in riding and the martial arts of swordsmanship and archery.
He was given his first military assignment when barely 12 years old. A Muslim tribe, the Ranghars of Nuh, had attacked and looted a Sikh Sangat (congregation) coming from the Pothohar region of northwest Punjab. Guru Gobind Singh sent Ajit Singh in command of 100 men to the village, which was a short distance from Anandpur across the River Satluj. Ajit Singh reached the village on 23 May 1699, recovered the looted property and punished the offenders.
In 1700 Anandpur was attacked by hill chiefs assisted by troops provided by the Mughal faujdar of Sirhind. Guru Gobind Singh had erected five Qila (forts) on the outskirts of the city. Ajit Singh, assisted by Bhai Udai Singh, a seasoned soldier, was put in charge of the defence of the Qila Taragarh Sahib. On 29 August the hill chiefs made the fort the target for their first attack, which was successfully repulsed. For four days the chiefs attacked the fortresses around the citadel, without success.
On 15 March 1701, a Sikh Sangat coming from the Darap area (near Sialkot) was waylaid by Gujjars and Ranghars. Sahibzada Ajit Singh led a successful expedition against them.