No one knows who invented the spitball, (multiple individuals have been credited) but one thing is for certain: Pitchers have been trying to gain any edge over batters since the game's early days. Though 19th century rules prevented players from defacing baseballs, penalties for doing so were weak and regulations were very rarely enforced by umpires. In the first two decades of American League play, those restrictions were ignored or forgotten altogether.
Jack Chesbro of the New York Highlanders was among the first to gain success by doctoring the baseball, winning 41 games in 1904. Ed Walsh of the White Sox used "the wet one" to fashion the lowest career ERA of all-time at 1.82. By 1910, pitchers were using any means necessary to deface the ball with mud and tobacco being the most commonly employed methods.
With pitchers enjoying a number of unfair advantages, managers voted to partially ban the spitball in the winter of 1919-'20. After the tragic Ray Chapman incident of 1920 (in which the Indians' shortstop was struck in the head and killed by a Carl Mays offering), the pitch was universally outlawed with the exception of a handful of hurlers who were allowed to throw it under a grandfather clause.
Moundsmen continued to tamper with balls anyway, employing various deceptive techniques. In 1942, Leo Durocher fined Bobo Newsom for throwing spitballs and lying to him about it. During his prime years of the 1950s, Whitey Ford was known to cut or scuff balls to get them to break more dramatically. Gaylord Perry, who arrived on the scene during the 1960s, used the spitter to assemble a Hall of Fame career. He proclaimed his innocence until 1974, when his autobiography was published.
Since most pitchers prefer to outwit batters by more conventional means, the act of doctoring the ball has remained a relatively rare occurrence. Even so, there was an inexplicable rash of scuffing incidents as recently as 1987. On August 3rd of that year, Minnesota's Joe Neikro got caught with a nail file on the mound and was thrown out of a game against the Angels. AL President Bobby Brown rejected the argument that he was innocently filing his nails on the bench and suspended the hurler for ten days. A week later, Philadlephia's Kevin Gross was ejected in the fifth inning of a game against the Cubs when sandpaper was discovered inside his mitt. He too was suspended for ten days and his glove was impounded by league officials.
Sporadic incidents have occurred into the 21st century, the most infamous being the controversial "Smudge-gate" fiasco during the 2006 World Series, in which Tigers hurler Kenny Rogers was accused of applying a foreign substance to balls during a 23-inning scoreless postseason stretch. As long as there are rules, there will always be rule-benders. For certain, we haven't heard the last of baseball's deceptive ball doctors.