Someone in my office says the character's gender was not defined; I thought Yoda was clearly male. Which one is it?
The Empire Strikes Back script treats Yoda as male:
LUKE: I'm not looking for a friend, I'm looking for a Jedi Master.
CREATURE: Oohhh. Jedi Master. Yoda. You seek Yoda.
LUKE: You know him?
CREATURE: Mmm. Take you to him, I will. (laughs) Yes, yes. But now, we must eat. Come. Good food. Come.
With that, the creature scurries out of the clearing, laughing merrily. Luke stares after him. All he sees is the faint light from the small power lamp moving through the fog. Luke makes his decision and starts after the creature.
I don't remember where I read about it but George Lucas apparently planned to have a female of Yoda's species in the prequels and I'm sure I've seen CGI mock ups for said character, this clearly says to me that Yoda is, in the eyes of the character's creator at least, male.
In Star Wars Rebels "Path Of A Jedi," Master Yoda seems to be a girl. For example, in the beginning it's like this
KANAN: You're lucky I'm not my master. SHE wouldn't let you-
EZRA: Get away with everything you tried to get away with.