Harry Leroy Halladay III (born May 14, 1977), usually referred to as Roy or his nickname "Doc", is a Major League Baseball starting pitcher for the Toronto Blue Jays. His nickname, coined by former Blue Jays announcer Tom Cheek, is a reference to Wild West gunslinger "Doc" Holliday. He was the Blue Jays' first draft selection in the 1995 Major League Baseball Draft, the 17th pick overall, and has played for the team since 1998.

Born in Denver, Colorado, Halladay grew up in the suburb of Arvada; his father was a pilot for a food processing company, while his mother was a homemaker. From an early age, Halladay loved baseball, trying every position on the field until, by age 14, his success on the pitcher’s mound attracted the attention of major league scouts. In 1995, after graduating from Arvada West High School, he was selected by the Toronto Blue Jays in the amateur draft. Six seasons in the minors later, the strapping right-hander made the team and immediately proved his worth.

In his second career start, against the Detroit Tigers on September 27, 1998, Halladay had what would have been the third no-hitter ever pitched on the final day of a regular season broken up with two outs in the ninth. The feat would have joined the combined no-hitter by four Oakland Athletics pitchers (Vida Blue, Glenn Abbott, Paul Lindblad and Rollie Fingers) in 1975 and Mike Witt's perfect game in 1984. The bid was broken up by a Bobby Higginson solo home run. The home run was the only hit Halladay would allow in a 2–1 Blue Jays victory, as he notched his first major league win.