Chicago is a rock band that was formed in 1967 in Chicago, Illinois. In the band's debut, they began as a politically charged, sometimes experimental rock band headed by the three-headed monster of singer/guitarist Terry Kath, singer/bassist Peter Cetera and singer/keyboardist Robert Lamm.

The band featured an unusual and unusually versatile line-up of instrumentalists, including saxophonist Walter Parazaider, trombonist James Pankow, and trumpet player Lee Loughnane, along with more traditional rock instruments — guitarist Terry Kath, keyboardist Robert Lamm, drummer Danny Seraphine, and bassist Peter Cetera (who was the last to join the original group).

The bands original name was 'The Big Thing', which changed to 'Chicago Transit Authority' when their first album "The Chicago Transit Authority" was released. Soon after the album's release, the band's name was shortened to simply 'Chicago', when the actual Chicago Transit Authority threatened legal action.

After Kath's death on January 23, 1978,(and the release of their 9th studio album, Chicago Xi), the band began to explore a softer sound that resembled more the style of 80s pop bands than the jazz-rock fusion that they began with. The reinvented sound produced many hit songs in the 80s, forever settling Chicago as adult contemporary favorites.

In 1985, Cetera insisted that they take a break from touring so that he could concentrate on a solo album and spend more time with his family. After the band rejected his offer to stay in the band while recording a solo album, it was announced that Cetera and Chicago would go their separate ways in July 1985. Cetera was replaced by bassist/singer Jason Scheff.

Despite the personnel changes over the years, the group still keeps active more than three-and-a-half decades after its founding. They are one of the few major rock groups that has never broken up or even taken an extended hiatus, although with original frontmen Kath and Cetera long gone, the group sometimes seems like an ensemble calling itself Chicago. Nevertheless, four of the six founding members (major songwriters Lamm and Pankow, plus Loughnane and Parazaider) remain to this day providing continuity, while Bill Champlin has put in over 25 years with the band, Jason Scheff over 20, Tris Imboden with 15 and Keith Howland having 11.

They had a steady stream of hits throughout the 1970s and early 1980s, such as:
1969: "Questions 67 and 68" - US#71 - sung by Cetera
1970: "Make Me Smile" - US#9 - sung by Kath
1970: "25 or 6 to 4" - US#4 (UK#7) - sung by Cetera
1972: "Saturday in the Park" - US#3 - sung by Cetera/Lamm
1974: "Wishing You Were Here" - US#11 - sung by Kath/Cetera
1976: "If You Leave Me Now" - US#1 (UK#1) - sung by Cetera
1982: "Hard to Say I'm Sorry" - US#1 (UK#4) - sung by Cetera
1984: "Hard Habit to Break" - US#3 (UK#8) - sung by Cetera/Champlin
1984: "You're the Inspiration" - US#3 (UK#14) - sung by Cetera
1989: "What Kind Of Man Would I Be?" - US#5 - sung by Scheff/Champlin

Discography:
The Chicago Transit Authority (1969)
Chicago (1970)
Chicago III (1971)
Chicago V (1972)
Chicago VI (1973)
Chicago VII (1974)
Chicago VIII (1975)
Chicago X (1976)
Chicago XI (1977)
Hot Streets (1978)
Chicago 13 (1979)
Chicago XIV (1980)
Chicago 16 (1982)
Chicago 17(1984)
Chicago 18 (1986)
Chicago 19 (1988)
Twenty 1 (1991)
Night & Day Big Band (1995)
Chicago XXV: The Christmas Album (1998)
Chicago XXX (2006)
Chicago XXXII: Stone of Sisyphus (2008)
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Chicago is also the name of a successful musical, made into a film starring Catherine Zeta Jones, Renee Zellweger and Richard Gere.