Tennis is a racket sport where players strike a felt-covered rubber ball over a net, aiming to make it impossible for the opponent to return it. The game's ancient roots trace back to 12th-century France, with King Louis X known as the first player by name, but the modern form of lawn tennis emerged in Birmingham, England, in the late 19th century. Remarkably, the rules have changed little since the 1890s, with the major exceptions being the adoption of the tiebreak in the 1970s and the introduction of Hawk-Eye electronic review technology in 2006. The sport's pinnacle is the four Grand Slam tournaments: the Australian Open (hardcourt), the French Open (clay), Wimbledon (grass), and the US Open (hardcourt). Tennis was one of the original Olympic sports and has been a permanent part of the Summer Games since 1988, while also being uniquely accessible to wheelchair users and the visually impaired. Today, it boasts millions of recreational players worldwide, and its popularity was boosted historically by the invention of the lawn mower in 1830, which enabled the creation of modern grass courts.