Cardinal George Resignation: Chicago Archbishop Submits Mandatory Letter (VIDEO)

Cardinal Francis George on Monday marked his 75th birthday, an important milestone for Catholic bishops.

As ABC Chicago reports, all bishops are required, upon their 75th birthday, to submit a letter of resignation to the pope -- although the pope, in turn, does not necessarily need to accept that resignation right away.

The resignation, instead, is somewhat of a formality as George is expected to remain in his post, at the head of the Chicago Archdiocese, for two or three more years, according to NBC Chicago. George is the first Chicago archbishop to reach 75 years of age.

(Scroll down to watch a report on Cardinal George's resignation letter.)

In an interview with the Chicago Tribune, George described the letter of resignation as "formula almost." Eligible to continue to participate in papal elections until the age of 80, the bishop expects to discuss his retirement with Pope Benedict when he travels to Rome with a group of Midwestern bishops in February.

"I am eager to be the first Archbishop of Chicago to retire!" George, a cancer survivor, said, according to WBEZ.

George has, meanwhile, begun the early stages of transitioning the archdiocese toward a new archbishop's leadership. Earlier this month, he named a new chief operating officer among other changes to local governance.

Formerly the president of the U.S. Conference of Catholic Bishops, George has run into controversy in recent months, most notably when he compared some LGBT activists to the Ku Klux Klan, a comparison he apologized for this month on the heels of many community leaders calling for his resignation.

George also came under some scrutiny in November, when the Catholic Conference of Illinois criticized Gov. Pat Quinn's decision to present an award to a rape survivor at a pro-choice luncheon, though George later backed away from the conference's statement.

Nevertheless, the cardinal has been popular among many Chicago Catholics. One parishioner described him as "an amazing man" to ABC and said she hoped he wouldn't be retiring anytime soon.

WATCH Cardinal George discuss whether he will retire soon: