Flint is a troll in the Ankh-Morpork City Watch recruited to the Watch and militia from the Ankh-Morpork Armoury during the events of Men at Arms. In Feet of Clay, he is part of Detritus' anti-Slab campaign. He was made Sergeant by Fred Colon during his short and tumultuous reign as Captain of the force (in The Fifth Elephant). Flint seems considerably less apt at being a sergeant than Detritus is, and it is unclear whether Flint has been able to keep his rank.
Flint is a hard, sedimentary from of Quartz, nodules of which are found in chalk and limestone.