The last emperor of the Western Roman Empire was Romulus Augustulus. His reign is traditionally marked as ending in 476 AD, which is often cited as the fall of the Western Roman Empire.

Here's a detailed explanation:

Step 1: Understanding the Context
By the 5th century AD, the Roman Empire had been divided into Eastern and Western halves for administrative purposes. The Western Empire faced severe crises including economic troubles, invasions, and political instability.

Step 2: Romulus Augustulus
Romulus Augustulus was proclaimed emperor in 475 AD by his father, Orestes, who was a military commander. He was very young, likely a teenager, and his name is somewhat ironic: "Romulus" after the legendary founder of Rome, and "Augustulus" meaning "little Augustus" (Augustus was the first Roman emperor).

Step 3: The End of His Reign
In 476 AD, Odoacer, a Germanic chieftain, led a revolt against Orestes, captured and executed him, and then deposed Romulus Augustulus. Rather than killing the young emperor, Odoacer sent him into exile in Campania (Italy) with a pension. The Roman Senate sent the imperial insignia to the Eastern Roman Emperor Zeno, effectively acknowledging that there was no longer a separate Western emperor.

Final Answer: Romulus Augustulus was the last emperor of the Western Roman Empire, deposed in 476 AD.