Taking to the the throne at age 16, following the death of his father Muteesa I of Buganda in 1884, Mwanga ruled as the Kabaka (king) of Buganda from 1884 until 1888 and from 1889 until 1897. The 31st Kabaka of Buganda, he would eventually be captured by colonial British forces and exiled to the Seychelles where he would eventually die in 1903.
He is most notably known for his aggressive expulsion of encroaching Christian missionaries in his kingdom by ordering Christian converts to either abandon their religion or face death.
Two months into his reign, and oblivious of the negative reactions from imperial powers on his action, Mwanga censured all foreign religions, labelling them dangerous and destructive to Buganda. He saw the burning to death of three Christian converts; and also ordered the capture of Alexander Mackay and two of his fellow Protestant missionaries.
Three years after ascending the throne in 1884, Mwanga had ordered the burning of 45 of his pages; 32 of the murdered converts would later gain worldwide recognition as the Uganda Martyrs.
The executions, including of Bishop James Hannington in 1885, alarmed the Protestants and Catholics, who despite their potent religious disputes, allied to dethrone Mwanga; and they did on August 2, 1888 with the help of the Muslims.
By the time of his first ouster from the throne, Mwanga had no major group to support him. The Muslims were not on his side, after he refused to convert to Islam; the Christians didn’t shield his back either—for ordering several executions; and the Traditionalists, convinced that the small pox ravaging the kingdom then was a result of neglect of traditional cultures and beliefs, had little faith in the king.
The most crucial threat to Mwanga’s reign would, however, be the Europeans, who had the same year he ascended the throne in 1884, met in Berlin, Germany, to allot Africa among themselves. Although he knew that the ‘white man’ was intent on ‘eating’ his kingdom, Mwanga was clueless about the extent of their imperial appetite and greed.
After his deposition, Mwanga was replaced by his brother Kiweewa—but just like his brother, Kiweewa refused to face the circumcision knife and the Muslims - the strongest group then, united to depose him, 40 days into his reign.
Further reading: Wikipedia*
*This source makes reference to same-sex relations that the Kabaka may have had, which is how I came to know of him (I was watching a televised debate on whether homosexuality is un-African and one of the speakers mentioned this incident). What I do not appreciate is the way in which some sources (linked source elaborates on this) have used his sexuality as something that is synonymous with evil, or the leading catalyst that led to him ordering the execution of several Christians.