Max Showalter was born in Caldwell, Kansas, the son of Elma Roxanna (Dodson) Showalter (1889-1953), a music teacher, and Ira Edward Showalter (1887-1953), who worked in the oil industry and was also a banker and farmer. He developed a desire for acting as a toddler while accompanying his mother to local theatres where she played piano for silent movies. By the late 1930s, he had multiple stage roles under his belt, and soon made his Broadway debut in Knights of Song. Showalter also appeared as a drag queen in the traveling musical This Is the Army for two years and in other notable Broadway productions like Make Mine Manhattan and The Grass Harp. His most memorable stage role was as Horace Vandergelder in the Broadway hit show, Hello Dolly!. Showalter performed the role more than 3,000 times opposite Carol Channing, Betty Grable and Ethel Merman. In the late 1940s, Max Showalter was signed to 20th Century Fox as a featured contract player. His name was changed by Fox’s founder, Darryl F. Zanuck to the more “bankable” Casey Adams. He made his feature film debut in Always Leave Them Laughing (1949). He first appeared on live television in the short-lived musical variety series The Swift Show (1948–49), also known as the The Lanny Ross Show. Showalter’s second feature film was the biopic With a Song in My Heart (1952), where he had a small role as a vaudeville performer. In the film, Showalter, along with (rumored lover) David Wayne, sang the song “Hoe that Corn”, which he also wrote. He appeared in Niagara (1953) alongside Marilyn Monroe and Joseph Cotten. He made a cameo as a Life magazine photographer in another Monroe movie, Bus Stop, in 1956.

During the 1950s, Max Showalter appeared in television shows like The Loretta Young Show and Navy Log, in addition to films like Vicki (1953), Down Three Dark Streets (1954), Naked Alibi (1954), and Indestructible Man (1956). The following year, he appeared as Ward Cleaver in the original pilot for the 1950s sitcom Leave It to Beaver. He was replaced by Hugh Beaumont for the television series.[4] Casey Adams also appeared in one episode of The Andy Griffith Show as an antiques dealer. His name is Ralph Mason in the episode titled “The Horse Trader.” In the 1960s, Showalter reclaimed his original name and continued to land roles in such big-budget films as Elmer Gantry (1960), The Music Man (1962), and How to Murder Your Wife (1965). He worked through the 1960s and 1970s. He made six appearances on Perry Mason, including the role of murderer Carl Reynolds in the 1958 episode, “The Case of the Curious Bride,” murder victim Burt Stokes in “The Case of the Wandering Widow” in 1960, and murderer Talbot Sparr in the 1964 episode, “The Case of the Ugly Duckling.” He made appearances in other television series like The Twilight Zone (the episode “It’s a Good Life”), The Lucy Show, Hazel, Surfside 6, The Doris Day Show, The Bob Newhart Show, Lord Love a Duck, Sgt. Pepper’s Lonely Hearts Club Band, and a short-lived 1980 TV series, The Stockard Channing Show. In the 1979 film 10, he played a pastor whose hobby was writing songs. Showalter made his last onscreen appearance in the film Sixteen Candles (1984). On July 30, 2000, Max Showalter died of cancer in Middletown, Connecticut. He was 83 years old.