Or my favorite* some history on the casting of Wakko:
Of the Warners, the voice of Wakko was the most difficult to cast. During auditions, the producers said they were looking for “wacky,” so all the actors delivered a voice that was over-the-top crazy, but none were the right fit. On the last day of auditions, Ruegger brought his 1990 Almanac to the office, hoping to find some inspiration that might shake things up. Many wacky Wakko’s later, they still didn’t have the right voice. So during their last appointment of the morning, with voice actor Jess Harnell, Ruegger opened the almanac to a list of celebrities and asked Harnell to do his best impression of Elvis, Rodney Dangerfield, Jackie Gleason, Frank Sinatra, and other notable names. When the Beatles came up, Harnell proceeded to do every one of the Fab Four so well you could actually tell which individual band member he was mimicking at the moment. However, it was Harnell’s Ringo that struck a chord with the producers, so after a few tweaks, that became the voice of Wakko.
Click the source link below for the whole post, warning its long but worth it.
Another one of my favorite skits from Animaniacs (You'll notice the voice is that of Motel 6's Tom Bodett)
Source -> http://www.mentalfloss.com/blogs/archives/126115
*My favorite is when one is able to watch the real-life voice actor doing the voice they're famous for, yes I'm 12.