Diarist (noun)

A person who keeps a diary or journal, especially one that is written regularly.

Origin:

From diary, meaning "a daily record of personal events, experiences or observations".

Examples:

1. She was a prolific diarist, her journals covering decades of her life.
2. He was a famous diarist and his journals were later published as a book.
3. She kept a diary in which she recorded her thoughts and feelings.
4. The diarist's daily entries provide a window into life in the 19th century.
5. The diarist's observations provide valuable insight into the historical events of the time.