Some of them seem pretty much in line with what you'd
expect; lightweight, medium weight, heavy weight. It was introduced as a class
between light heavy and heavyweight. Heavyweight has historically not had a
weight maximum while light heavy has generally been set at around 180 (178
under current rules). Up until the late 70's cruiserweight was used merely as a
catch weight because most heavyweight champions such as Joe Louis or Rocky
Marciano were under 200 pounds, but as boxers got bigger the need for a new
weight class became evident.
