Cuellar and Denny McLain each won the AL Cy Young Award in 1969, due to a tie in the voting.

Cuellar, nicknamed "Crazy Horse" because of his superstitious nature, ranks among Baltimore's top five career leaders in wins (143), strikeouts (1,011), shutouts (30) and innings pitched (2,028).

Not interested in pursuing that as a career, Cuellar joined the Cuban Army, which allowed him to play baseball on weekends.

[2] In the 1950s, the Cincinnati Reds executed a working agreement with the Havana Sugar Kings of the Triple-A International League (IL), helping them acquire many Cuban players, including Cuellar.

[2] Entering the 1959 season, Cuellar was featured on a baseball card in a Topps set for the very first time, though the company misspelled his name as "Cueller.

In his two innings of work, Cuellar surrendered a grand slam to Gene Freese in the third and a two-run double to Al Schroll in the fourth.

[10] One of these came in the second game of a doubleheader against the Pittsburgh Pirates; Cuellar allowed five runs in 7+1⁄3 innings but earned the win (his first) in a 12–5 Cardinal victory.

[15][17] Cuellar ultimately won his first six decisions, the last a 3–2 complete game over the Cardinals at the Astrodome on June 25, in which he recorded a career-high 15 strikeouts.

[20][21] On September 10, he and Don Drysdale of the Dodgers held each other's teams scoreless through nine innings; Cuellar took the loss when he gave up a run in the 10th.

[2] In Cuellar's final start of the campaign, a 4–3 road win over Cincinnati in the second match of a September 28 twi-night doubleheader, he hit his first major-league home run, off Sammy Ellis, to lead off the top of the fifth.

During the ninth, Philadelphia manager Gene Mauch called him a name from the dugout, hoping to start a fight and get both players ejected.

[10][29] After the major league seasons, Cuellar had typically played winter baseball in Latin America over the offseasons.

[10] On December 4, the Astros traded Cuellar, Enzo Hernández, and Tom Johnson to the Baltimore Orioles for Curt Blefary and John Mason.

The Orioles went on to sweep the Twins three games to none en route to winning the American League Pennant and earning a berth in the World Series against the New York Mets.

However, he contributed offensively in the fourth inning, when he hit a pitch from Jim Perry that barely stayed fair as it passed over the right field fence for a grand slam.

[30] Cuellar had a rocky start in Game 2 of the 1970 World Series against the Reds, lasting only 2+1⁄3 innings and giving up four runs (though only one was earned).

It was then that his pitching coach, George Bamberger, advised Cuellar to stop throwing his screwball for the rest of the game.

Cuellar settled himself down and followed Bamberger's advice by relying on his fastball, curveball, and changeup, to shut out the Reds for the next eight innings for an impressive 9-3 complete game victory that clinched the World Series title for the Orioles.

Forty years later, reporter Mike Klingaman wrote, "Of his 185 big league victories, none meant more than that World Series win to Cuellar.

"[44] Facing the Indians in his second start of the year on April 14, 1971, Cuellar only struck out two batters but only allowed four hits in a 3–0 shutout win.

Earlier in the year, Cleveland manager Alvin Dark had said that Cuellar's fastball "couldn't blacken an eye.

[64] He shut out the Milwaukee Brewers on June 4, then held the Minnesota Twins to one run in a complete game, 2–1 victory five days later.

[63] Teammate Pat Dobson was so impressed with Cuellar's success, he started wearing his socks for good luck.

[68] Palmer and McNally each won 20 games again, and newcomer Dobson did so as well, making the Orioles the first team to have four twenty-game winners since the 1921 Chicago White Sox.

[10] After a one-year absence from the playoffs, the Orioles won the AL East again, facing the defending World Series Champion Athletics in the ALCS.

[89] On August 15, he struck out a season-high 10 batters and held the White Sox to six hits and one run in a complete game, 2–1 victory.

[87] In early September, Cuellar, Palmer, McNally, and Ross Grimsley set an AL record with five consecutive shutouts.

[10] Cuellar was a "junkball" pitcher, relying heavily on his excellent screwball and change-up rather than a hard fastball, according to Baltimore Sun reporter Mike Klingaman.

[44] Usually he displayed a quiet personality and worked quickly on the mound, but struggles could occasionally cause him to lose his temper.

He stayed in the dugout until his catcher put his gear on, refused to step on the foul line, and refrained from signing autographs on days he was pitching.