While most of the characters in this are fictional, William "Bigfoot" Wallace was a real person, he is one of the most famous real life Texas Rangers. In real life he survived the "Black Bean Incident" and went on to command his own unit of Texas Rangers. He later participated in the Mexican-American War Battle of Monterrey and the Comanche Wars. During the Civil War he helped defend the Texan frontier against Comanche attacks. He actually survived all these battles and died of natural causes in 1899 at the age of 82.
The expedition that this film centers around, while containing fictional characters, is based on a real expedition ordered by President of Texas Mirabeau Lamar to annex New Mexico to the Republic of Texas in 1841. The use of black and white beans to decide who to execute and who to spare is borrowed the Mier expedition, which took place the following year.
Buffalo Hump was a real person, he was the leader of the Comanche nation at the time this takes place. He is most famously known for leading the Great Raid of 1840. In response to the government of the Republic of Texas slaughtering many of the leaders of the Comanche nation under the false pretense of meeting to discuss terms for a treaty, Buffalo Hump lead 400 Comanche warriors and attacked settlements stretching from the plains of west Texas all the way to the Gulf of Mexico. It is the single largest raid carried out by Native Americans on white cities, and the only Native American raid in Texas to reach all the way to the ocean.