Siddhartha Dhar

Abu Rumaysah al-Britani, born Siddhartha Dhar (24 June 1983) also known as Jihadi Sid, is a British citizen who is an Islamic State (IS) militant. On 3 January 2016, he was named as the lead executioner in a film issued by IS from Raqqa, Syria that showed the execution of suspected British spies against the Islamic State. Rumaysah had been called the second 'Jihadi John', due to his British accent and appearance in the film. Abu Rumaysah has been designated as a global terrorist by the United States.

Dhar was born in London to a Bengali-speaking Hindu family of Indian origin and changed his name to Abu Rumaysah after his conversion to Islam. He acted as a spokesperson for the Islamist group Al-Muhajiroun, an organisation banned in the UK, and worked as an aide to Al-Muhajiroun's co-founder, Anjem Choudary. Dhar also owned a bouncy castle rental company. He lived in Walthamstow. He used social media to promote his Islamist views and attended demonstrations in Britain against the United States, Israel, and Arab governments. In a video he posted to YouTube, Dhar described IS's self declared caliphate as "...a dream for all Muslims worldwide ... We can finally have a sanctuary where we can practice our religion and live under the sharia. It is a big, big thing". and their at the time four children, later arriving at Syria.

As of 2025, Dhar's current whereabouts are unknown. He is either still missing or presumed dead.