Zapp-Leela relationship

The relationship between Zapp Brannigan and Turanga Leela is a recurring theme on Futurama.

Development
The initial beginnings of this relationship starts in "Love's Labours Lost in Space", where Leela, out of pity, sleeps with Zapp Brannigan. Interestingly, before this event, Leela was actually a fan of Brannigan, but when Brannigan tries to win her back, she becomes furious with him.

On the other hand, Zapp becomes very cocky after having slept with Leela, and would so, on further occasions, constantly believe he still has a chance. The relationship (and the event) was referenced numerous times by Bender in the first and second season. After that it purely becomes a joke appearing less and less.

In the comics, Zapp occasionally loses interest in Leela, to which Leela actually becomes upset.

In "The Beast with a Billion Backs", Leela walks in on Zapp and Amy in bed together but only shows brief shock (any opinions are interrupted by Yivo's tentacles).

In "In-A-Gadda-Da-Leela", Leela and Zapp were lost together at Lo'ihi Island. Zapp made Leela believe they were on another planet and that they were out of water so she accedes to make love. Leela then realized Zapp was lying, but they later were forced to make love by V-GINY to save Earth.

In "Zapp Dingbat", Zapp starts dating Leela's mother, Munda. While Leela doesn't show any jealousy, she is convinced that Zapp is using Munda to get to her. She attempts to seduce him to prove he's only interested in her but the plan fails. Munda later breaks off their relationship after finding out Zapp’s true nature.

In “Fun on a Bun”, Zapp interacts with Leela at Oktoberfest, briefly reminding her of their previous sexual encounters.

While Zapp does not seem to show sexual interest in Leela by "Zapp Gets Cancelled," they do interact again, with Zapp saying she's a terrible cook.

Appearances

 * Episodes where their actions between these characters based on the event, as well as references by other characters.