Hitting for the cycle is a relatively rare feat. To accomplish a cycle, a player must get a single, double, triple, and home run in the same game. A four-hit game is rare enough, but to include each of the four hits is a significant feat. In fact, it is on par with a no-hitter in rarity.
A "natural cycle" is hitting a single, double, triple and home run in order in a game. Obviously, it is even rarer.
Four players have hit three cycles in their career: Long John Reilly, Bob Meusel, Babe Herman and Adrian Beltre. Beltre was the latest to join in 2015 when he hit his third. 30 players have hit for the cycle twice. In 2012, Aaron Hill hit two cycles in a span of 11 days, joining Herman who had hit two cycles in 1931 (but over two months apart). Three players have hit for the cycle in both leagues: Bob Watson, John Olerud and Michael Cuddyer.