After Brenda Blethyn (the 1st choice to play Christine Baskets) was unavailable, Zach Galifainakis and Louis CK had a meeting to discuss new options. Zach asked Louis what he was thinking, and CK said "I'm thinking of a voice (pause) it sounds like Louie Anderson". Zach said they should reach out to Anderson and explain the role. When Anderson said "I'll just play her as if she's my mother", they knew they'd found the right actor for the role.
Zach Galifianakis has said that Dale is an "effeminate racist", a character type that he has used generally in his stand-up along with specific material about his (non-existent) twin brother Seth. He said that Dale may be a closeted homosexual but his nastiness is used as a cover to not only deflect away any homophobia but to prevent anyone from countering his rude, ignorant, and thoughtless actions.
The show had initially and understandably planned to cast a female actress to play Christine Baskets. However, several initial casting attempts didn't work, so Zach Galifianakis and Louis CK decided to pause the process and brainstorm. Galifianakis asked CK "What voice do you think of when you think of Christine?" CK thought for a minute and said that as crazy as it sounded, he heard the voice of Louie Anderson. The two men immediately realized that was perfect and put together an offer for Anderson to take the role without auditioning, which he accepted.
Zach Galifianakis stated that Dale was based on longtime stand-up/performative comedy character "the effeminate heterosexual". He saw Dale as an insecure person who was preemptively mean and insulting to everyone around him so they wouldn't pick on him first.