While the exact reason is unknown, there are several theories regarding why Nathaniel Hawthorne changed his last name. For example, some historians speculate that Nathaniel changed his last name from Hathorne to Hawthorne simply to change the way his surname was pronounced.
Others, including Nathaniel’s granddaughter, Hildegarde Hawthorne, believe he changed the spelling of his last name to match the way his ancestors used to spell the family surname before immigrating to America. Alternately, it is believed that Hawthorne changed his surname to set himself apart from certain members of his family who used the surname Hathorne. This theory is backed up by the fact that Hawthorne distanced himself from his family's strong Puritan beliefs in his writings, including "The Scarlet Letter."
From the time he was born until some time after he graduated college, Nathaniel spelled his last name Hathorne. While Nathaniel used the last name Hawthorne almost exclusively later in life, he never changed his name on any official records. However, his name appears as Hawthorne on several of his most famous literary works, and this is the spelling most often used today when referencing Nathaniel Hawthorne.
According to Vernon Loggins, author of the book “The Hawthornes,” Nathaniel’s sisters adopted the changed spelling of his surname, while his mother continued to use Hathorne. In addition to going by his full name, Nathaniel Hawthorne also used the nickname Hath when corresponding with friends and acquaintances.