Roller skates are shoes, or bindings that fit onto shoes, that are worn to enable the wearer to roll along on wheels. The first roller skate was effectively an ice skate with wheels replacing the blade. Later the "quad" style of roller skate became more popular consisting of four wheels arranged in the same configuration as a typical car.
The first patented roller skate was introduced in 1760 by Belgian inventor John Joseph Merlin. His roller skate wasn't much more than an ice skate with wheels where the blade goes, a style we would call inline today. They were hard to steer and hard to stop because they didn't have brakes and, as such, were not very popular. The initial "test piloting" of the first prototype of the skate was in the city of Huy, which had a party with Merlin playing the violin.
In the 1840s, Meyerbeer's Opera, Le prophète featured a scene in which performers used roller-skates to simulate ice-skating on a frozen lake set on stage. The result was to popularize roller skating throughout the Continent. As ice skaters subsequently developed the art of figure skating, roller skaters wanted the ability to turn in their skates in a similar fashion.
In 1863, James Plimpton from Massachusetts invented the "rocking" skate and used a four-wheel configuration for stability, and independent axles that turned by pressing to one side of the skate or the other when the skater wants to create an edge. This was a vast improvement on the Merlin design that was easier to use and drove the huge popularity of roller skating, dubbed "rinkomania" in the 1860s and 1870s, which spread to Europe and around the world, and continued through the 1930s. The Plimpton skate is still used today.
Eventually, roller skating evolved from just a pastime to a competitive sport; speed skating, racing on skates, and inline figure skating, very similar to what you see in the Olympics on ice. In the mid 1990s roller hockey, played with a ball rather than a puck, became so popular that it even made an appearance in the Olympics in 1992. The National Sporting Goods Association statistics showed, from a 1999 study, that 2.5 million people played roller hockey. Roller Skating was considered for the 2012 Summer Olympics but has never become an Olympic event. Other roller skating sports include jam skating and roller derby. Roller skating popularity exploded during the disco era but tapered off in the 80s and 90s.