Zachary Fardon would replace Patrick Fitzgerald, who stepped down last summer to enter private practice. Fitzgerald rose to national prominence during more than a decade in the office and successfully convicted two Illinois governors, including Ryan. The U.S. Senate must confirm President Barack Obama's nomination of Fardon.
Both of Illinois' senators, Democrat Dick Durbin and Republican Mark Kirk, support the choice.
"Zachary Fardon will be an exceptional U.S. Attorney for the Northern District of Illinois," Durbin said in a news release announcing the nomination. "I spoke to him today and advised him that he'll have to hit the ground running and immediately focus on daily gang and gun violence plaguing the streets of Chicago."
Kirk called Fardon "an outstanding pick to continue Patrick Fitzgerald's tradition of aggressively prosecuting criminal activity that threatens northern Illinois."
The post is widely regarded as Chicago's second-most powerful job, after the mayor. The chief prosecutor and around 170 assistant attorneys also have an impact beyond Illinois, including by handling major terrorism cases.
Fardon, a partner at the Chicago law firm Latham Watkins, was on the team of federal prosecutors who secured convictions against Ryan in 2006. In that case and in others, Fardon gained a reputation as an adept, quick-witted cross-examiner.
Fardon also served in the U.S. attorney's office in Nashville, Tenn., and later entered private practice. Among his clients was John Wyma, a longtime lobbyist and friend of former Illinois Democratic Gov. Rod Blagojevich, whose testimony helped convict Ryan of corruption.
Fitzgerald's shoes would be large ones for anyone to fill.
The lanky, soft-spoken lawman from New York arrived in Chicago with a mandate to clean up corruption-plagued Illinois, and he had helped put several public officials behind bars, including Blagojevich.
The Obama administration made its selection from four finalists: Fardon, Lori Lightfoot, Jonathan Bunge and Gil Soffer. Their names were forwarded to the White House by Durbin and Kirk, who vetted a longer list of prospective candidates.
Any of the four would have known their way around the federal prosecutor's office in Chicago - one of the nation's busiest - each having worked there as assistant attorneys.
Fitzgerald was a surprise pick for the job in 2001. At the time, he was co-chief of the organized crime and terrorism unit for the U.S. attorney's office in the Southern District of New York.
Fitzgerald spearheaded the investigations that put both Ryan, a Republican, and Blagojevich, a Democrat, in prison on corruption convictions. Fitzgerald also helped send dozens of other city and state officials to prison.
Leading up to the announcement of Fitzgerald's replacement, many legal observers said appointing someone with close Chicago ties could convey confidence that the city is no longer as corrupt as it was. Others wondered if it might signal a desire to shift the focus from corruption to other crime, such as drug trafficking or gang-related murders.
Still, public corruption was one of the matters all four finalists thought should be among the office's concerns, co-chairs of a screening committee for the U.S. senators wrote in a letter describing interviews with the four. The letter said all four also cited violence and drugs; financial crimes; and terrorism, though not necessarily in that order, as primary matters of concern for the office.
Federal investigations can take years before they result in indictments or go to trial, so any shift in direction is likely to be incremental.
As Fitzgerald racked up flashy convictions - including those of reputed mobsters and terrorists - he gained a reputation as a no-nonsense prosecutor who erred on the side of secrecy and typically eschewed banter with reporters. He could be tenacious to a fault, defense attorneys said. Over the years, many complained that Fitzgerald pursued their clients with too much fervor, loading indictments up with as many charges as he could muster.