In which season did Dan Butler become main cast as Bulldog?

Dan Butler became a main cast member as Bulldog in season 4 of Frasier.

Butler first appeared as Bob “Bulldog” Briscoe in the first season, when the character was introduced as the loud, abrasive sports-radio host whose show followed Frasier’s program on KACL. At first, Bulldog was recurring rather than part of the principal cast. His popularity and frequent clashes with Frasier made him increasingly important to the station’s ensemble.

Season 4 marked the change in billing: Butler was listed among the starring cast alongside Kelsey Grammer, Jane Leeves, David Hyde Pierce, Peri Gilpin, and John Mahoney. Bulldog remained a main cast member through seasons 4–6, even though he continued to appear in a different pattern from the central Crane family.

A common mix-up is to treat his first appearance as the same thing as his promotion to the main cast. Those dates are different. After Bulldog was fired from KACL at the end of season 6, Butler’s appearances became occasional again, though the character returned at intervals later in the original series.