Prior to the television show 'I Love Lucy,' in what old time radio show did Lucille Ball star?

Lucille Ball starred in "My Favorite Husband" with Richard Denning on July 5,1948.

My Favorite Husband was first broadcast as a one-time special on CBS Radio on July 5, 1948. CBS's new series Our Miss Brooks had been delayed coming to the air, so to fill in the gap that week CBS aired the audition program (the radio equivalent of a television pilot) for My Favorite Husband. Lucille Ball and Lee Bowman played the characters of Liz and George Cugat, and a positive response to this broadcast convinced CBS to launch My Favorite Husband as a series. Bowman was not available to do the series, so when it debuted later that month it starred Lucille Ball and Richard Denning as the leads. The couple lived at 321 Bundy Drive in the fictitious city of Sheridan Falls, and were billed as "two people who live together and like it." Beginning with the 26th episode on January 7, 1949, confusion with bandleader Xavier Cugat prompted a name change Cooper. It began as a sustaining program, but around the same time as the name change Jell-O became the sponsor.

"I love Lucy" first aired on television on October 15, 1951.