The RSS (Rashtriya Swayamsevak Sangh) is the ideological grandparent of the Sangh Parivar, and remains its most important organisation. Founded in 1925 by K. B. Hedgewar, it has well-documented historical links to European fascism and a history of involvement in violence against minorities and attacks on cultural targets such as film festivals.
The RSS were central in the assassination of Gandhi, though they tactically distanced themselves from Gandhi's assassin, Nathuram Godse, afterwards. They have links with recent terrorist attacks with evidence some were planned with the knowledge of senior RSS members.
The RSS operates several front organisations abroad, such as the Hindu Swayamsevak Sangh (HSS), which raises funds for the RSS via "charitable donations" in the UK. Narendra Modi began his political career as a full-time RSS worker and, like many Sangh Parivar leaders, remains a member.
References
• Articles on the RSS on Communalism Watch and Kafila.