Bing Crosby was an American singer and actor. At the time the First Doctor, Sara Kingdom and Steven Taylor crashed a film set, he was a clown. He was depressed because Charlie Chaplin had trademarked the good gags. (TV: The Daleks' Master Plan)
Later, the Third Doctor was once serenaded by the Brigadier, a fan of Crosby's, who was badly attempting to recreate Crosby's signature tune, "White Christmas". (PROSE: Smash Hit) Peri Brown told the Fifth Doctor that she wanted a Christmas on Earth, which had, among other things, Bing Crosby singing "White Christmas". (PROSE: Far Away in a Manger)
In 2008 Bea Nelson-Stanley played one song of Bing Crosby on her old record player. (PROSE: Eye of the Gorgon) Erimem and Andy Hansen listened to a recording of Crosby singing "The Twelve Days of Christmas" on 25 December 2016. (PROSE: Damn You, Bing Crosby)
Behind the scenes
Crosby's appearance in the show marked the first time in Doctor Who's run that a living figure would appear played by someone else.