R5-D4 was the little
astromech droid that
Uncle Owen and
Luke Skywalker were going to buy in Star Wars: A New Hope. But the
droid was
defective, and blew a circut.
"Unlce Owen, this R2 unit has a bad motivator," said Luke. (actually, Luke, that's an R5 unit...not that anyone excpet
die hard Star Wars geeks care)
This prompted
C-3PO to suggest to Luke that they instead purchase
R2-D2, which they did, and the rest is history.
Footnote: some lame
Darkhorse Comic wrote a
story about R5-D4, calling him
Skippy the Jedi Droid. In the story, it claims that R5-D4 had a high concentration of
midichlorians in the oil greasing his parts, thus giving him
Jedi powers. However, he foresaw the
future, and realized that it was R2-D2's
destiny to deliver the
Death Star Plans in order to save the
Universe. So R5-D4 purposely blew his motivator so that R2 could be purchased instead.
I'm not making this up....