Larry Fowler is a human male and a host of the talk show "The Larry Fowler Show". His show is first mentioned in Grave Peril and Fowler himself is first mentioned in Summer Knight. Fowler then appears in Death Masks hosting a special. Fowler and the lawsuit he brings against Harry Dresden is something of a running gag throughout the series.
The studio audience began to chant, "Lah-REE, Lah-REE, Lah-REE!— 
Larry Fowler is a short man who wears glasses and an immaculate suit, always smiling for the camera.
In the series
In Death Masks, Fowler introduces Harry Dresden in his "The Larry Fowler Show" on live television. He manages to put Dresden in a number of awkward positions, asking about his relationship with the Special Investigations of the Chicago Police Department, and demonstrations of his magical abilities. He also introduces Father Vincent and Duke Paolo Ortega, who, among many technical problems plaguing the recording of the show, challenges Dresden to a duel. Fowler later has his lawyer sue Dresden for trashing his car and studio.
Dresden had already appeared on the show just after he'd gone into business as an investigator and that he'd had to fight against the infamy he received after that appearance.
In Blood Rites, when Karrin Murphy's mother remarks that she saw him on the The Larry Fowler Show, Harry Dresden confirms that the legal case is still ongoing. Dresden had to hire a lawyer, who doesn't think there is a good case, but it is expensive and time consuming.
I Was a Teenage Bigfoot
In "I Was a Teenage Bigfoot", Harry Dresden offers Strength of a River in His Shoulders an opportunity to clear things up about his people, claiming that he can get the Bigfoot on The Larry Fowler Show anytime he wants.
In Proven Guilty, Harry Dresden mentions to Karrin Murphy that he thinks a PI may be following him due to the still ongoing lawsuit. He states that Fowler can really hold a grudge and keeps doing one thing after another.