[UPDATE: To be clear, Mark Twain was a rather notorious believer in infinite copyright. Just read his testimony for yourself, as linked below.]
Mark Twain testified before Congress in 1906. The bill he was testifying about was to extend the term of copyright in the United States to the life of the author plus fifty years. He said that this would satisfy any reasonable author because it would satisfy his own children. "Let the grandchildren take care of themselves," he said. An excerpt from his testimony is below.
My copyrights produce to me annually a good deal more money than I have any use for. But those children of mine have use for that. I can take care of myself as long as I live. I know half a dozen trades, and I can invent a half a dozen more. I can get along. But I like the fifty years' extension, because that benefits my two daughters, who are not as competent to earn a living as I am, because I have carefully raised them as young ladies, who don't know anything and can't do anything. So I hope Congress will extend to them that charity which they have failed to get from me.