Pearl's controversial recruitment of a McDonald's All-American in the late 1980s caused friction between the two programs that has remained ever since.
By the late 1980s, Iowa and Illinois had become two of the nation's best programs. If Indiana and Purdue didn't exist, they would've competed annually for the Big Ten championship.
Though the Hoosiers and Boilermakers traded (and sometimes shared) the Big Ten title each year, that didn't stop the Hawkeyes and Fighting Illini from establishing a heated rivalry. In fact, the frequent grappling to become the second-best program in the conference probably fueled the hatred the two teams had for one another.
Illinois was always a contender under longtime coach Lou Henson, but Iowa fell into mediocrity after Lute Olson left for Arizona in 1983. The rough patch didn't last long, however, as Dr. Tom Davis quickly brought the Hawkeyes back to national prominence with an Elite Eight run in 1986-87, a run that included a memorable 22-point comeback against the Illini on Jan. 14.
Both programs obviously didn't like each other - that's just college basketball - but everything changed in 1988. Then-Iowa assistant coach Bruce Pearl actively began recruiting Deon Thomas, a high school basketball superstar in Chicago. Thomas, a 1989 Illinois Mr. Basketball and McDonald's All-American honoree, had offers from programs all-over the country, but the growing prestige of Iowa and Illinois led most to believe he would remain in the Midwest.
Pearl's recruitment of Thomas was normal early-on, but it turned south when Thomas revealed to Pearl that Illinois made several illegal offers to him, which included $80,000 dollars and a new apartment for his grandmother. Rather than tell the NCAA what Thomas said, Pearl turned into Sherlock Holmes and investigated on his own, which turned into a disaster.
According to the official court document, Fred Mims, an Associate Athletic Director and Iowa's NCAA compliance officer, provided Pearl with a tape recorder to record phone calls. Pearl responded by calling Thomas "at least 10 times" in the spring of 1989, where the two continued to talk about Illinois' offers to Thomas. Pearl then played the tapes to various members of the NCAA and a University of Illinois attorney.
Though Pearl hoped his findings would win him his prized recruit, Thomas still ended up playing for the Illini from 1990-1994, where he became the school's all-time leading scorer. Despite Thomas' efforts, Illinois failed to reach the second weekend of the NCAA tournament, which was directly because of Pearl.
Pearl's investigation surprisingly didn't reveal that Illinois committed any wrongdoing while recruiting Thomas, but it did show some other violations the Fighting Illini broke several years earlier. As a result, Illinois was punished with limited recruiting and a postseason ban in 1990-91 - Thomas' freshman season in Champaign.
Thomas always resented Pearl for his actions, evidenced by this 2012 quote from the Alton Telegraph.
"For a while, I was angry," Thomas said of the NCAA investigation and its outcome. "(Pearl) took a lot away from Coach Collins [Illinois assistant coach] myself and from Illini Nation. If that didn't happen, maybe we would have made it back to the Final Four the next year. Who knows? He put a black eye on the program."
Pearl later apologized to Thomas and several members of Illinois' coaching staff that same year, but the Pearl/Thomas incident ultimately jumpstarted the heated rivalry we now know today.
Though Illinois leads the overall series by a comfortable 94-77 margin and has won nine of the last 10 meetings over the Hawkeyes, Iowa is hoping new coach Ben McCollum can turn the tide back to the Hawkeyes.
The next chapter of this great rivalry tips off Sunday, when the No. 19 Hawkeyes play host to the No. 16 Fighting Illini. The game is set to begin at 11 a.m. CST on FOX.