Final answer:
William B. Travis wrote his letter to Henry Smith, the governor of the provisional government of Texas, seeking support and reinforcements to defend the Alamo.
Step-by-step explanation:
William B. Travis wrote his letter to a fellow Texan named Henry Smith.
Travis addressed the letter in this way because Smith was the governor of the provisional government of Texas at the time.
Travis hoped that Smith would provide support and reinforcements to defend the Alamo during the Texas Revolution.