Matt Soniak sums up the reasoning of eight classic authors:
George Orwell: When Eric Arthur Blair was getting ready to publish his first book, Down and Out in Paris and London, he decided to use a pen name so his family wouldn’t be embarrassed by his time in poverty. He chose the name George Orwell to reflect his love of English tradition and landscape. George is the patron saint of England and the River Orwell, a popular sailing spot, was a place he loved to visit.
Lewis Carroll: While Lewis Carroll might sound delightfully British to American ears, Charles Lutwidge Dodgson is even more so. Dodgson adopted his pen name in 1856 because, according to the Lewis Carroll Society of North America, he was modest and wanted to maintain the privacy of his personal life. When letters addressed to Carroll arrived at Dodgson’s offices at Oxford, he would refuse them to maintain deniability. Dodgson came up with the alias by Latinizing Charles Lutwidge into Carolus Ludovicus, loosely Anglicizing that into Carroll Lewis and then changing their order. It was chosen by his publisher from a list of several possible pen names.