On December 10, 1838, Mirabeau B. Lamar was sworn in as president of the Republic of Texas.

http://www.tsl.state.tx.us/treasures/giants/lamar/lamar-01.html

In 1834, Lamar decided to visit Texas, where his friend James Fannin had recently moved and begun slave trading in Velasco. Lamar fell in love with Texas and decided that he too would make it his home. Like Fannin, he became a passionate revolutionary. Lamar went home to Georgia to settle his affairs for the move, only to learn of the massacres at the Alamo and at Goliad, where Fannin and 341 other Texas revolutionaries had been taken prisoner and executed by orders of General Santa Anna.

Lamar rushed back to Texas and joined the revolutionary army as a private. He was commissioned a colonel on the field of San Jacinto just before the start of the battle and made commander of the cavalry. During the battle, he distinguished himself by his bravery and quick action. After the Texan victory, Lamar was made secretary of war in the cabinet of President David G. Burnet, and in the fall of 1836 was elected vice-president of the Republic of Texas.

Lamar became a political opponent of President Sam Houston. In 1838, Houston could not by law run for another term. Lamar ran for the office himself and won. On December 10, 1838, Mirabeau B. Lamar was sworn in as president of the Republic of Texas.