Mike Judge, the creator, provides the voices of the Hank Hill as well as the mumbling ladies' man Boomhauer. Judge previously provided voices for, and wrote for, Beavis and Butt-head. He was also the voice of Kenny in South Park: Bigger Longer & Uncut. You've seen him in Office Space and Spy Kids.
Kathy Najimy is probably very familiar to you, even beyond being the voice of Peggy. She has been seen in many TV shows and films. Her most successful projects include Sister Act, Hocus Pocus, Veronica's Closet, Wall-E and Rat Race.
Pamela Segall Adlon
Though Bobby Hill is a clever young boy, he is voiced by a woman named Pamela Segall Adlon, who won an Emmy for her performance in my favorite episode "Bobby Goes Nuts." After a short stint as Kelly Affinado on The Facts of Life, Adlon has enjoyed a lengthy career as a voice actor. She has provided voices for characters in Rugrats, FernGully: The Last Rainforest, The Oblongs and other cartoons.
Stephen Root voices the character of Bill Dauterive. Stephen Root is no stranger to animated TV. He has also provided voices for Tripping the Rift and American Dad. He has worked with Mike Judge since the film Office Space. He has also starred in Newsradio, According to Jim and True Blood.
Lauren Wong is no stranger to voiceover work. Not only does she do the voice for Minh on King of the Hill, she is also Amy Wong on Futurama. Most famously, she was Ross's girlfriend Julie on Friends.
Tom Petty is most-well known as a Grammy-winning musician, playing with Tom Petty and the Heartbreakers as well as the Traveling Wilburys. Lucky for us he is also the voice of, well, Lucky, on King of the Hill.
Ashley Gardner is the voice of Nancy Gribble, Dale's weather-person wife. She has also appeared on many TV shows, including an iconic turn as the librarian on "The Library" episode of Seinfeld.
Johnny Hardwick provided the voice of neighbor Dale Gribble for the entire run of King of the Hill. He also served as a sometimes writer and producer, as well. The animators are said to have drawn Dale Gribble to look like Johnny Hardwick.