Theodor Mommsen, the eminent 19th century German philologist, legal scholar and historian, gained his early reputation through the collecting of Latin inscriptions, Corpus Inscriptionum Latinarum (see also) as source work for the until then almost exclusive ancient literary knowledge of the Roman antiquity, as well as coins. His two major works in his prime were Roman Constitutional Law and Roman Criminal Law. He was a foremost innovator in the study of Roman history, which would never be the same thereafter.
He was a sometime journalist, '48 revolutionary – he spent a couple of years in exile in Zürich, Switzerland, the same time as Richard Wagner, whom he detested, life long liberal with active political involvement; a rude polemicist who did not suffer fools gladly and made many enemies (including his son-in-law, the graecist Ulrich von Wilamowitz-Möllendorf); a brilliant administrator, organizer and fund raiser, poet, frequenter of literary and intellectual salons; father of 16 children, 12 of whom survived infancy.
To the general public, he became best known through his Roman History, for which he received the Nobel Prize for Literature in 1902.This work is greatly shaped by his "sometimes passionate judgment" and his own political experiences.
A complete translation of the 'Roman History' is now online: Theodor Mommsen - History of Rome. However, a warning: navigation around the site is not the easiest, and the first three chapters can be found in an easier set-up at Ancient / Classical History at About.com. The printed edition in English is hard to get.
Of interest to our current book discussion on Sulla is Book 4, The Revolution.
Mommsen never wrote a history of the emperors, and it is not clear whether or not he ever intended to. However, transcriptions of his lectures were discovered in 1980, edited and published, eventually in the English translation too: A History of Rome Under the Emperors.