While Travis Hafner's minor-league numbers foretold some major-league success, they certainly did not reveal the type of success Pronk has enjoyed the past two seasons. In 2005, he finished 5th in MVP voting, quite a feat for a full-time DH. He lead the league in OPS+ (remember, the Jake has been playing as a pitcher's park lately), 2nd in unadjusted OPS, 3rd in slugger, etc, etc.
Travis Hafner is probably in the prime of his career. He's 28, but only has 1321 at-bats in the majors. So any comparative system is going to be off a bit, since a lot of Hafner's comparables had much more experience by age 28. Still, there are some interesting names in baseball-reference's similar players for Travis Hafner:
(1) "1B" Dick Stuart
Known as "Dr. Strangeglove" for his defensive ineptness at first base, Stuart was in the lineup for his bat. At age 28, he hit .301/.344/.581 for the Pirates, and blasted 35 home runs. He posted a couple more productive seasons with the Red Sox, and was pretty much done at age 32. Unfortunately for Stuart, he retired before the advent of the Designated Hitter.
Stuart was also known for his quips. One example:
Stuart - who apparently had a reputation as a bit of a night owl, during his previous seasons with the Pittsburgh Pirates (including their 1960 World Champion, on which team Stuart split first base time with Rocky Nelson) - raised a hand, and Pesky acknowledged it. "Is that tax deductible?" Stuart asked. "And with that," Radatz said, "everybody fell off their stools in the clubhouse."
(2) OF Brian Giles
Perhaps it was karmic justice for John Hart to deal away Giles when with Cleveland and to send Hafner to Cleveland a couple years later. While the physical aspects of the two players are dissimilar, their early career patterns are quite striking in their similarities.
You know the story with Giles: the Indians had a loaded outfield when Brian was coming through the system, and when Hart picked up David Justice after Albert Belle left, the writing was on the wall. Unfortunately, Hart traded Giles not for an ace pitcher but a left-handed reliever. His first season in Pittsburgh, the first season that Giles was a full-time player, he hit .315/.418/.614 for the Pirates. And he's still going strong at age 34.
(3) 1B Jim Gentile
Gentile was stuck behind Gil Hodges in the Brooklyn/LA system for eight years before he finally got traded to Baltimore in 1960. He rewarded the Orioles with two exceptional season in '60 and '61. In 1961 he hit 46 home runs (but finished third in the AL behind two guys named Mantle and Maris), and posted a .302/.423/.646 line. That was his high-water mark, but he was productive through age 30.
(4) 1B Reggie Jefferson
The "other" player in the Omar Vizquel/Felix Fermin deal after the 1993 season, Jefferson found a home in Boston, where he hit .347/.388/.593 in 1996 for the Red Sox. He followed that performance in 1997 with a .319/.374/.520 line, but that was the last season Jefferson would get 400 at-bats.
(5) 1B Joe Hauser
Hauser broke into the big leagues at age 23 and had his best season at age 25, when he hit 27 homers (second to Babe Ruth). Hauser broke his knee in 1925, missed the entire season that year, and wasn't the same afterwards.
(6) 1B/OF Ron Bloomberg
The first designated hitter in major-league baseball, Bloomberg suffered from injuries his entire career. His best season was in 1973, when he hit .329/.395/.498 for the Yankees. He was out of baseball by age 30.
(7) 1B Gordy Coleman
Coleman had all of 15 at-bats with the Indians before being traded to the Reds for Johnny Temple. Gordy became the Reds' starting first baseman, putting up good numbers in 1961 and 1962. Unfortunately for him, the Reds brought up Tony Perez in 1964, and the young Cuban took over first base for good in 1967.
(8) 1B Bill Terry
The lone Hall of Famer in the group. Terry was the last National Leaguer to hit .400, and was the Giants' main offensive weapon during much of the late 1920s and early 1930s. He also was blocked as a young player; future Hall of Famer George Kelly was the culprit in this case. Because of Kelly, Terry didn't get much playing time until he was 26.
(9) 1B Lyle Overbay
A perfect contemporary with Hafner, Overbay is just five months Travis' senior. Lyle also didn't get a real chance until he was 27. Hafner has been the better offensive player, but Overbay is the better defender.
(10) OF Bob Johnson
"Indian Bob" was a mainstay for the Athletics after winning the left field job in 1933. He hit 20 home runs for nine consecutive years for Philadelphia and made eight All-Star teams. He was a productive player through age 39, hitting .280/.358/.425 in 1945 for the Red Sox.