Final answer:
John Slidell was the president responsible for the annexation of Texas.
Step-by-step explanation:
The president responsible for the annexation of Texas was John Slidell. He was sent as an emissary by President Polk to Mexico City to resolve the border dispute and also to secure California and New Mexico for the United States. Slidell's mission to buy Mexican territory was met with opposition from the Mexican press, and he was ultimately sent away.