The 17th-century English diarist famously associated with New Year's resolutions is Samuel Pepys.
Pepys kept his celebrated diary from 1660 to 1669, recording Restoration-era London with unusual detail. In an entry dated 31 December 1661, he described taking a solemn oath to abstain from plays and wine, a clear example of the self-improvement promises now associated with New Year's resolutions.
Pepys wrote in a shorthand system partly because the diary was intensely private. It chronicles much more than personal discipline: his work at the Navy Office, domestic life, theatre-going, political events, the Great Plague and the Great Fire of London all appear in its pages. The diary was not published in full until the 19th century, long after Pepys's death.
A common mix-up is that Pepys was not the only early diarist to record resolutions. Anne Halkett's 1671 diary contains an entry titled “Resolutions,” making her an important earlier documented example. Even so, among the choices—and in popular historical references—Pepys is the intended answer.