Frank Cannon was originally a policeman, but he quit the force after the tragic death of his wife and infant son in an automobile accident. The tragedy drove Cannon to become a top private eye.
In the pilot of the series, Cannon drove a Lincoln Continental Mark III. The car was wrecked by the bad guys in an attempt to scare Cannon off the case. Then, for most of the series, Cannon barreled around in a Lincoln Continental Mark IV. During the last part of the series' run, the chubby private eye's Cannonmobile was the Lincoln Continental Mark V.
The license plate for Frank Cannon's "Cannonmobile" was "963-XUJ"
The mobile number for the phone in Cannon's car was 213-191-9221.