Literal FF, both for his leadership in securing Texas' independence and for his loyalty to the Union during the Civil War.
Didn’t Texas as an independent country literally exist to dodge Mexico’s laws against slavery?
Slavery aggravated exiating tensions, but as the bear flag revolt later on shows Anglo immigrants, especially the illegal squatters later on never took the pledge of alliegance to Mexico seriously, so some sort of revolt was probably inevitable, slavery or not.
That is not to denigrate the legacy of Stephen Austin however, who undertook the project to settle Texas in good faith, and helped quell insurrectionary sentiment several times before. His mistreatment, as well as his federalist leanings did lead to disillusionment towards the end of his life. Santa Anna's betrayal of his previous federalist ideals proved to be the last straw for many, as the revolts in Yucatan and Zacatecas show, and his brutal response to the latter only served to further terrify the ideologically liberal Anglo settlers. Again it's difficult to see how a coup ridden and authoritharian Mexico was going to inspire loyalty ftom Texans.