Who among the following is exclusively associated with diary writing in English?

The correct option is Samuel Pepys.

To understand why this option is correct, let us look at the literary contributions of the writers listed:
1. Samuel Pepys (1633–1703): He is one of the most famous diarists in English literature. His private diary, which he kept from 1660 until 1669, provides a detailed, first-hand account of major historic events in London, such as the Great Plague of London and the Great Fire of London. In English literary history, his name is almost exclusively and famously associated with the art of diary writing.
2. Samuel Johnson (1709–1784): He was a celebrated essayist, poet, biographer, and lexicographer, best known for compiling A Dictionary of the English Language.
3. Ben Jonson (1572–1637): He was a major Jacobean playwright and poet, famous for plays like Volpone and The Alchemist.
4. Samuel Richardson (1689–1761): He was an English writer and publisher, best known for his epistolary novels like Pamela and Clarissa.

Therefore, Samuel Pepys is the figure exclusively associated with diary writing in English among the choices provided.