Samuel Pepys: The Unequalled Self, by Claire Tomalin. Knopf, 448 pages, $30.

No one agrees on when the modern era began. The 17th century, when Francis Bacon heralded the rise of science? The rise of a literate middle class in the 18th century? Or 1789, when the French Revolution led to the secular state? Claire Tomalin thinks that the modern era began Jan. 1, 1660, when Samuel Pepys began writing literature's most celebrated diary. That diary, she says, shows Pepys to be the first modern man.

Unlike the Puritan diarists who preceded him, Pepys does not appear much interested in the examination of conscience. Rather, Tomalin says, he "looked at himself with as much curiosity as he looked at the exterior world," with a scientific detachment of the observer who writes from the self who acts.

He observes everything. He marks the events of the wider world -- the Restoration, the plague in London and the Great Fire of 1666. In public life, he is the man of business administering the Royal Navy (Tomalin sees another aspect of his modernity in his discovery that "work is one of the major pleasures of life") and buying barrels of oysters. In the private world, we see the worries about health and money, discord with his wife, and his persistent but frequently fruitless pursuit of other women.

All is recorded in a matter-of-factness that fascinates. He knows how to construct literary narrative, how to show himself in a comic as well as a serious light, but it is in his candor that Tomalin finds the source of his appeal: "Pepys found himself so entertaining that he did not want to miss anything out. His self-portrait, warts and all, is compelling enough to draw us in and makes us live uncritically inside his skin. Moving fast through the events of each day and the crowds of people with whom he had dealings, his energy burns off blame, making it surprisingly hard to disapprove of him."

Pepys discontinued the diary in 1669. The text, written in a private shorthand, survived untranslated until two editions, neither entirely satisfactory, were produced in the 19th century. It was not until the edition by Robert Latham and William Matthews in 1970 that a complete, reliable edition was available.

Tomalin moves beyond the diary to track Pepys though the last 34 years of his life, making use of public records, his surviving letters, a later, more perfunctory diary. Pepys remained loyal to the Stuart monarchy, even after James II fled England at the Glorious Revolution of 1688. He continued to be involved with the Royal Society. He lived vigorously until his health finally gave out. It was a full life.

Though nothing quite matches the diary itself, Tomalin's biography captures the fascination of Pepys' personality. Her efforts to locate him in the context of his time and place succeed admirably, as does her effort to identify him as "a hero of an altogether new kind," an explorer who made "discoveries of the complex relations between the inner and outer worlds of a man."

John E. McIntyre, The Sun's assistant managing editor for the copy desk, studied the literature of the Restoration and 18th century at Syracuse University. He keeps no diary.