Flag of Confederate guerrilla fighter William Quantrill. Born in Ohio Quantrill found himself in Kansas at the outbreak of the war and joined Missouri troops led by Sterling Price. Quantrill felt Price wasn't aggressive enough and left the army to become a guerrilla fighter in Kansas.
Quantrill, along with 30 men, invaded the Kansas town of Aubry, followed by Olathe. His most famous raid was leading 300 men into Lawrence, Kansas, on August 21, 1863. After the Lawrence raid 150 men lay dead and over 200 homes and businesses were destroyed. In October of that year Quantrill and his men struck Baxter Springs, attacking the fortification there and leaving 90 soldiers dead.
Quantrill found himself heading east in 1864, and a month after Lee's surrender he was killed while skirmishing with Union soldiers in Kentucky. William Quantrill died in Louisville, KY just shy of his 28th birthday.
While Quantrill was not known to carry a flag, this flag and similar ones became popular in the 1880's. A small First Confederate patterned flag was found after the Olathe raid, however who carried it and why remains a mystery.