As it turns out there are quite a few people that were or are known to use fountain pens:

• Mark Twain

IIRC, Mark Twain also lost a considerable amount of money investing in an early typewriter company.

searches

Apparently he was also a very early user of typewriters.

https://historyfacts.com/arts-culture/fact/mark-twain-first-typewriter-book/

I was the first person in the world that ever had a telephone in his house,” Mark Twain once claimed, adding that he was also “the first person in the world to apply the typemachine to literature.” The author born Samuel Clemens was indeed the first to publish a book written on a typewriter, though he may have misremembered which one it was — Twain recalled it being The Adventures of Tom Sawyer, but it was more likely 1883’s Life on the Mississippi, according to typewriter historian Darryl Rehr. Twain didn’t type the book on a typewriter himself, however — he handwrote it and the manuscript was later typed.

The typewriter in question was a Remington 2, which the company later told the public about as part of a marketing campaign. In an advertisement published in Harper’s, Remington published a letter that Twain wrote, in which he made this observation about the emerging technology: “At the beginning of that interval a type-machine was a curiosity. The person who owned one was a curiosity, too. But now it is the other way about: the person who doesn’t own one is a curiosity.”