The link above leads to a website on Rootsweb of an interview in 1937 of a man, James RUSSELL, born in 1868 who once lived in the Going Snake District of Indian Territory. He mentions having known or heard of several SIXKILLERs:
"Among the old-timers who lived in this community were, Frog SIXKILLER, Johnnie WALKER, Wash LEE, Tom SWAKE, Wilson BUSHYHEAD, Smith BUSHYHEAD, John BLACKFOX and Soldier SIXKILLER. These men always helped the Russell family harvest."
He goes on to mention SIXKILLERs in connection with the War Between the States and as stockmen dealing in cattle.