What is the first name of baseball's McLain?

The first name of baseball’s McLain is Denny.

Denny McLain, whose full name is Dennis Dale McLain, was an American right-handed pitcher best known for his remarkable career with the Detroit Tigers. He made his Major League Baseball debut with Detroit in 1963 at age 19 and played ten major-league seasons from 1963 through 1972.

McLain’s defining achievement came in 1968, when he went 31–6 for the Tigers. He became the first major-league pitcher since 1934 to win at least 30 games in a season, and he remains the last pitcher to reach that mark. That season brought him the American League Most Valuable Player Award and the Cy Young Award, while Detroit went on to win the World Series.

The name “Denny” is the familiar form associated with him in baseball records and coverage, although “Dennis” appears in biographical information. He won a second consecutive Cy Young Award in 1969, sharing it with Baltimore pitcher Mike Cuellar, and finished his career with 131 wins.