Riri Yaka

Riri Yaka, or Reeri Yakseya, is a figure of Sinhalese belief, called the demon of blood in 19th-century accounts from Ceylon and blamed above all for illnesses that cause bleeding.

The earliest record here is John Callaway's 1829 English translation of the Yakkun Nattannawa, a Sinhalese poem describing Ceylon's demonology. Its index lists Rirey Yakseya as the demon of blood.

Dandris de Silva Gooneratne, in On Demonology and Witchcraft in Ceylon (1865), called Reeri Yakseya the cruellest and most powerful of the group he was describing. He wrote that Riri Yaka is shown with a monkey's face on a man's body, with fiery red skin, riding a red bull. He said Riri Yaka was thought to play a part in nearly every disease a Sinhalese person could suffer, and to cause in particular those that bring a flow of blood.

Wikipedia ranks Riri Yaka second only to Mahasona in cruelty and power in Sinhalese folklore, and repeats the monkey head, red skin and red bull. It says he is believed able to cause every kind of illness, with haemorrhages and blood diseases especially put down to him.