William Lee Miller's Arguing About Slavery: John Quincy Adams and the Great Battle in the United States Congress includes a nice collection of quotes about John Caldwell Calhoun. The Harriet Martineau quote is well known - in fact I've cited it before - but the others may be less familiar:
Calhoun was a major figure not only in South Carolina but in national politics as well. The modern historian David Potter has called him "the most majestic champion of error since Milton's Satan." The English reformer Harriet Martineau, who became acquainted with him on her visit to the United States in 1835, wrote - a famous quotation - that Calhoun was "a cast-iron man, who looks as if he had never been born and could be extinguished." James Henry Hammond, who hoped to be the Calhoun of his generation, said in Charleston on the occasion of Calhoun's death in 1850 that "Mr. Calhoun had no youth, to our knowledge. He sprang into the arena like Minerva from the head of Jove, fully grown and clothed in armor: a man every inch himself, and able to contend with any other man."
Hammond's eulogy, claiming almost every virtue for his subject, did twice concede that Calhoun had no wit or humor. The historian Merrill Peterson, writing in the late twentieth century, said of Calhoun: "Intensely serious and severe, he could never write a love poem, though he often tried, it was later said, because every line began with 'whereas.'"