Udham Singh (Punjabi: ਉਧਮ ਸਿੰਘ, Hindi: उधम सिंह्; December 26, 1899 – July 31, 1940), born Sher Singh Jammu, (Kamboj) ,  was an Indian independence activist, best known for assassinating Michael O'Dwyer in March 1940 in what has been described as an avenging of the Jallianwalla Bagh Massacre.
Singh was also known as Ram Mohammed Singh Azad, symbolizing the unification of the three major religions of India: Hinduism, Islam and Sikhism. Singh is considered one of the best-known of the more extremist revolutionaries of the Indian freedom struggle; he is also sometimes referred to as Shaheed-i-Azam Sardar Udham Singh (the expression "Shaheed-i-Azam," Urdu: شهید اعظم, means "the great martyr"). Bhagat Singh and Udham Singh along with Chandrasekhar Azad, Rajguru and Sukhdev, were the more famous names out of scores of young firebrand "freedom fighters" in the early part of 20th-century India. These young men believed their motherland would win her freedom only through the forceful removal of the British rulers. For their strong belief in the use of violent means to achieve India's freedom, a nervous England labelled these men as "India's earliest Marxists/Bolsheviks".
In 1940, almost 21 years after the Amritsar Massacre of 1919 in Punjab province of India, Singh shot dead Michael O'Dwyer at Caxton Hall in London. O'Dwyer had been Governor of the Punjab in 1919, when General Reginald Edward Harry Dyer ordered British troops to fire on unarmed Indian protesters, mostly Sikhs.