Guru Hargobind Sahib Ji, sixth Sikh Guru emerging from Gwalior Fort where he was imprisoned by Emperor Jahangir. Along with him, 52 Hindu chieftains were also released, on request from the Guru. Sikhs celebrate Diwali festival as “Bandi Chhor Diwas” because the Guru reached Amritsar back on the Diwali day. For the full story visit http://www.sikhiwiki.org/index.php/Bandi_Chhorh_Divas
Very few people know that this day is also important for Sikhs because of martyrdom of Bhai Mani Singh. He transcribed the final version of Guru Granth Sahib dictated to him by Guru Gobind Singh in 1704.