You could say that Rome was on the verge of falling from the time of its very first emperor, or you could say Rome fell in A.D. 410, 476, or 1453. You could even say that it hasn't yet fallen. Here are articles on emperors -- depending on your perspective, who may have contributed to the fall of Rome.
Portraits of Julius Caesar and the 1st 11 emperors of Rome.
Table of dates and data on the Flavian emperors, Vespasian, Titus and Domitian.
Portraits of 36 of the Roman emperors.
Table of the dates and manners of death of the generally short-lived and murdered emperors from Maximinus Thrax to Carinus.
Quiz: Chaos Emperors/Tetrarchy
Table of dates and data on the emperors who immediately followed Nero, Galba, Otho and Vitellius.
Table of dates and data on the emperors of Constantine's dynasty.
Julian the Apostate
When Julian came to power Christianity was less popular than paganism, but when the pagan Julian was killed in battle, it was the end of Roman official acceptance of polytheism.
Theodosius put an end to the heresies at Constantinople and was the last emperor effectively to control both East and West.
Valens' disaster at the Battle of Adrianople in the Eastern Roman Empire in A.D. 378, was one of the crucial events leading to the ultimate Fall of the Roman Empire.
Names and dates of major imperial battles, sieges, and civil wars.
Table of eastern and western Roman emperors after the death of Theodosius I.