Sam Clemens’s brother Henry did in fact die when the steamboat he was working on, the Pennsylvania, exploded. Sam had dreamed of Henry’s death a month earlier, and these experiences left him with an abiding curiosity about psychic phenomena and the other side: he was a member of the Society for Psychical Research. He was also curious about technological advancements, becoming a friend of the inventor Nikola Tesla and patenting three inventions himself.
In real life, like Richard Burton, Sam Clemens traveled to Salt Lake City and met Brigham Young, writing about the experience in his book Roughing It. His most famous comment on the Mormons he met, though, is probably this one, about polygamy:
“With the gushing self-sufficiency of youth I was feverish to plunge in headlong and achieve a great reform here – until I saw the Mormon women. Then I was touched. My heart was wiser than my head. It warmed toward these poor, ungainly and pathetically ‘homely’ creatures, and as I turned to hide the generous moisture in my eyes, I said, ‘No – the man that marries one of them has done an act of Christian charity which entitles him to the kindly applause of mankind, not their harsh censure – and the man that marries sixty of them has done a deed of open-handed generosity so sublime that the nations should stand uncovered in his presence and worship in silence.'”