early 19th century, was a highwayman who lived at Gleann 'a Ghadaí (valley of the robbers), Ballybackagh, some four miles north-west of Athenry, County Galway, Ireland.
Locally described as a big man and feared by his neighbours, Deois robbed people going to and from the Galway market, usually in the area between Cúinne Geal - near what is now Carnmore Airport - to Cussaun Cross on the Galway-Monivea road.
Deois was finally captured at the Cúinne Geal in the following circumstances: "A man and his son were on their way from Galway after selling a cart of hay.
The father, who didn't want to part with his money, grappled with Joyce and succeeded in getting him around to the rear of the horse cart.
Antoine Ó Raifteiri mentioned Casán Liam Deois in a poem about the musician Tomás Daly of nearby Coshla.