Final answer:
Mirabeau B. Lamar, the second president of Texas, advocated for the removal of Native Americans from their lands through a policy of ethnic cleansing initiated in 1839.
Step-by-step explanation:
The Texas leader who advocated for hostile treatment of Native Americans and sought their removal from their lands was Mirabeau B. Lamar, the second president of the Lone Star Republic. In 1839, Lamar instituted a program of ethnic cleansing aimed at pushing all Native American tribes out of Texas. His actions reflected the general contempt held by American settlers in Texas towards both Tejano and Native American residents during a period of intense conflict and territorial expansion.