Jim Backus Jim Backus ( 1913 - 1989 ) was a busy character actor in nearly every medium , but he is best remembered as the voice of cartoon star Mr . Magoo , as James Dean ' s father in " Rebel Without a Cause " , and finally as Thurston Howell III on " Gilligan ' s Island " . In April 1962 ( over two years before " Gilligan " ) , Backus was part of the ensemble cast playing international correspondents in the comedy / variety show pilot " Mad Mad World " , co - starring Jim Henson ' s Muppets . Years later , he was also on the list of actors considered for the part of editor Mike Tarkanian in " The Great Muppet Caper " ( 1981 ) , which went to first - choice Jack Warden . Backus began his acting career on the legitimate stage ( even appearing on Broadway ) , but soon drifted to radio , starting in New York in the late 1930s . He played bit parts on many dramatic series ( including " The Shadow " ) and appeared on soap operas ( playing son - in - law Dick Grosvenor on " Stella Dallas " ) . Gradually , Backus began appearing more often in comedy ( including bits on " The Jack Benny Program " ) , and increasingly using a voice he first used at parties . This was a snobbish , rich man characterization , used in a string of short - lived mid - 1940s series before finally finding a real home and a name : on " The Alan Young Show " beginning in 1944 and through 1949 , as Alan ' s friend / rival Hubert Updyke III . Hubert soon became a national sensation , and the sitcom was transferred to Hollywood in 1946 ( and Backus with it ) . Backus reprised Hubert Updyke in guest spots on Bob Hope ' s series and " Command Performance " , and played similar types on the shows of Danny Kaye , Eddie Cantor , Mel Blanc , and on " The Great Gildersleeve " ( replacing Gale Gordon as pompous neighbor Rumson Bullard ) . He very briefly headlined his own series as Updyke , " The Jim Backus Show " , in 1947 ( co - written by wife Henny ) . He was also heard on the dramatic series " Suspense " and " Richard Diamond , Private Eye " , among others . During his radio years , Backus gradually began playing supporting film roles , but first really gained notice as a voice actor in theatrical cartoons , including the 1948 Bugs Bunny short " A - Lad - in - His - Lamp " ( as the genie , ala Updyke ) . UPA hired him , and while he was heard in many of their shorts , he starred as Mr . Magoo beginning in " Ragtime Bear " ( 1949 ) and would reprise the role into television as late as the 1970s . His movie roles included turns in Universal ' s " Ma and Pa Kettle " and " Francis the Talking Mule " series , and he entered TV ( co - starring as Judge Bradley Stevens , the " I " in " I Married Joan " from 1952 until 1955 ) . Also in 1955 , Backus played his best dramatic part , ineffectual father Frank Stark opposite James Dean in " Rebel Without a Cause " . While Backus remained in demand as a supporting actor in movies , increasingly larger guest spots , and headlined his own self - named series again ( 1960 - 1961 ) , his next biggest break came in 1964 , with a series created by " Alan Young Show " writer Sherwood Schwartz : " Gilligan ' s Island " . Backus again dusted off the Hubert Updyke III characterization , but he was now rechristened Thurston Howell III , the millionaire , forever overshadowing the former and guaranteeing that most future guest roles would have " Special Guest Star " billing attached . After the series ended in 1967 , when not reprising Howell ( in reunion movies and two Filmation animated series , through 1982 ) or Magoo , he mostly remained active through guest spots ( including " The Brady Bunch " , " Gunsmoke " , and " The Love Boat " ) and occasional film turns ( including Disney ' s " Pete ' s Dragon " ) until slowed down by Parkinson ' s Disease .