Mr. Sweet was a small parasitic creature that appeared in the Doctor Who episode "The Crimson Horror". This creature came from a species of "red leech" that existed during Earth's Jurassic era and was a common threat to the Silurians during that period. Though the red leeches were believed to have gone extinct, they saw a revival at some point before the Victorian era and had evolved.
History[]
The creature that would become known as "Mr. Sweet" was discovered by Winifred Gillyflower at some point before 1893. The parasite had been living in a polluted river, surviving by feeding on human waste. Mrs. Gillyflower took the creature and allowed it to reside on her chest, feeding it while it in turn gave her its "nectar". Gillyflower named the creature "Mr. Sweet", possibly because it had developed a fondness for sugar.
In 1893, Mrs. Gillyflower planned to use Mr. Sweet's poison in a twisted plot for world domination. Founding the intentional community of Sweetville, Gillyflower invited those she deemed to be "perfect" to join her community where they could be safe from an impending apocalypse. Of course, Gillyflower planned on triggering this apocalypse herself by harvesting and mass-producing red leech poison, launching it into the atmosphere via a rocket and scattering it across the Earth. Fortunately, the Doctor, Clara Oswald and the Paternoster Gang were able to stop her.
Death[]
After Mrs. Gillyflower was fatally wounded from a fall, Mr. Sweet separated itself from her, no longer seeing her as a useful host. The Doctor considered taking Mr. Sweet back to the Jurassic era, but Gillyflower's daughter Ada furiously crushed the creature with her cane.