He was the starting catcher when the Twins won the 1991 World Series; Harper batted .381, the best among all regular Minnesota batters.

Despite his first seeing action for the Angels in 1979 and his hitting .350 with 28 home runs and 122 RBI for Salt Lake City in 1981, the Angels were not interested in giving Harper time behind the plate, at first base, or DH over established stars such as Rod Carew, Bob Boone, Don Baylor, and Reggie Jackson.

The Cardinals would go on to lose the game in the ninth 2-1 on the Royals' Dane Iorg's pinch-hit 2-run single following the infamous Don Denkinger non-out call on Jorge Orta.

Similarly, the other catchers that the Twins had tried in 1987, Tom Nieto, Mark Salas, and Sal Butera, did no better at the plate and were thus not seriously considered as replacements.

[2] Harper would have one of his best seasons in 1991, finishing with a .311 average, 10 home runs and 69 RBI, and would help to propel the Twins team to the memorable 1991 World Series win in seven games over the Atlanta Braves.

He endured a violent play-at-the-plate collision with Lonnie Smith early in the Series, holding onto the ball to preserve a run.

In the top of the 8th inning, Harper teamed up with first baseman Kent Hrbek to execute an outstanding 3-2-3 double play.

After the World Series win, Harper re-signed with the Twins for another two years, including arguably his best season in 1993 in which he would hit .304 with 12 home runs and 73 RBI, playing in a career-high 143 games.

Again granted free agency, Harper would not catch on with a team until 20 April 1995, when he returned to the A's, and his career would end nine days later after going hit-less in two games.

The Angels at that time were building entirely around free agents and veterans, in no mood to give a young player a chance.

After this, Harper served two years as a roving catching instructor in the San Francisco Giants organization.

On November 3, 2016, Harper was named the hitting coach of the Toledo Mud Hens, the Triple-A affiliate of the Detroit Tigers.

[5] Harper is also a coach for a youth travel baseball program called Trosky, in Scottsdale, Arizona, during the fall and winter months.

[7] Harper's older brother, Glenn, spent five years in the New York Mets' organization between 1972 and 1976, as both an outfielder and a pitcher, but did not advance beyond A ball.