- Sang and played bass for a Chicago-area rock band called the Apochryphals from 1964 to '69.
- Met his wife, Arlene, in high school; both appeared in a touring company of Hair in 1969, which was Mantegna's professional stage debut.
- In 1978, while with Chicago's Organic Theater Company, cowrote Bleacher Bums, which later played off-Broadway and was adapted for television by the Chicago PBS station (it won a local Emmy).
- Has appeared in six plays and movies written by fellow Chicagoan David Mamet, most notably Glengarry Glen Ross, for which he won a Tony.
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