Star Wars: 10 Things You Didn't Know About R2-D2

In The Empire Strikes Back, Luke gets a message from Ben Kenobi telling him to travel to the remote world of Dagobah to continue his Jedi training. The swamp planet isn't the best of places to visit, and Yoda isn't exactly what Luke was expecting a Jedi Master to be. The strange green alien tries to steal Luke's lamp, getting into a fight with R2-D2 and hitting the droid with his stick. 

This is a funny scene in its own right but it gets even better when you realize the two of them have met before, and actually have a personal history that stretches back more than two decades.

During season six of The Clone Wars, Yoda begins to have strange visions and is confined to the Jedi Temple. He knows he has to discover the reason for his visions, though, and sneaks out, escaping in a fighter with R2. During their adventures, they find the origin of the Force and discover how a Jedi's spirit can continue on after death.

Their journey eventually leads them to Qui-Gon's Force spirit on Dagobah, so not only do R2 and Yoda have a shared past, it's also not the first time the little droid has visited the strange, uninhabited planet.