Free-Staters was the name given to settlers in Kansas Territory during the "Bleeding Kansas" period in the 1850s who opposed the expansion of slavery. The name derives from the term "free state", that is, a U.S. state without slavery. Many of the "free-staters" joined the Jayhawkers in their fight against slavery and to make Kansas a free state.

Jayhawker and red leg are terms that came to prominence in Kansas Territory during the Bleeding Kansas period of the 1850s; they were adopted by militant bands affiliated with the free-state cause during the American Civil War. These gangs were guerrillas who often clashed with pro-slavery groups from Missouri, known at the time in Kansas Territory as "Border Ruffians" or "Bushwhackers". After the Civil War, the word "Jayhawker" became synonymous with the people of Kansas, or anybody born in Kansas. Today a modified version of the term, Jayhawk, is used as a nickname for a native-born Kansan.