The Fiery Hand is a group of slave soldiers employed as guards for the red temple of R'hllor in the Free City of Volantis. The Fiery Hand contains a thousand soldiers, never more and never less. Each of these soldiers is a slave of R'hllor. They wear ornate armor over their orange robes, and wield spears with points shaped as writhing flames. As per the custom of Volantis, these slaves have flames tattooed across their cheeks.
A Dance with Dragons
Soldiers of the Fiery Hand escort the priest Moqorro aboard the Selaesori Qhoran. Tyrion nicknames them "fiery fingers", as there are five of them. When Moqorro recites the nightly prayers to R'hllor before the nightfire, the guards lead the responses.
Only three of the fingers survive the storm that wrecks the ship. After the ship is captured by slavers, they are brought to the slave auction held outside of Meereen. Tyrion believes that the flames tattooed upon their faces will ensure some red temple will purchase them from the slavers.