I assume that you are asking about Montezuma II, and not Montezuma I, who was the great-grandfather of Montezuma II. Montezuma II is much more famous. Montezuma II was the Aztec emperor at the time of the Spanish conquest. He was killed in the process of that conquest.
Montezuma II was the 9th emperor of the Aztec empire. He led the empire as it expanded to its greatest size. However, it was also under his rule that the empire fell apart. This was because the Spanish, led by Hernan Cortes, invaded Mexico during the rule of Montezuma II. Montezuma was captured by the Spanish and was eventually killed. He was killed by stones thrown by Aztecs who were enraged at his conduct.
Montezuma II, then, is known as the last emperor of the Aztecs.