In the original Star Wars trilogy, was Yoda made using CGI available at that time or was he made using practical effects (like a puppet)?
The Yoda in the 1980 Empire Strikes Back and in the 1983 Return of the Jedi was entirely realised using puppetry.
Here we see Frank Oz (the chief puppeteer and voice of Yoda for the two movies):
And here's a video of the behind the scenes footage:
CGI in 1980 and 1983 was in no way capable of rendering anything like Yoda. Here is arguably the best effort of CGI from 1984:
Even when CGI was used for Yoda in the prequels, we see the result is good but still not quite so realistic as the original puppets:
The first real attempt to incorporate a CGI character in a movie was Terminator II (1991), more than a decade after the introduction of Yoda (1980).
Computers in 1991 were so primitive, James Cameron invented the liquid metal T-1000 because it was the only kind of CGI effect that wouldn't look awful a few years later — it was supposed to look fake.
But 90s CGI is usually pretty bad. George Lucas began redoing the original trilogy's special effects when he rereleased A New Hope for its 20th anniversary. The version on the left is the original Jabba puppet; the version on the right is the best 1997 CGI could do:
My personal dividing line for when CGI characters got realistic enough to be invisible is Rise of the Planet of the Apes (2011):
In the original trilogy (i.c. Episode V: The Empire Strikes Back, and Episode VI: Return of the Jedi, since in Episode IV: A New Hope Yoda doesn't make an appearance), Yoda was portrayed exclusively using puppets:
Frank Oz provided Yoda's voice in each film and used his skills as a puppeteer in the original trilogy and Star Wars: Episode I – The Phantom Menace. For some walking scenes in Episodes V and I, dwarf actors Deep Roy and Warwick Davis appeared in costume as Yoda [..]. While Frank Oz served as the primary performer, he was assisted by a multitude of other puppeteers [..].
The make-up artist Stuart Freeborn [who designed the character and created the puppet] based Yoda's face partly on his own and partly on Albert Einstein's.
(Here's a really nice insight into the character design, and how it turned out to be somewhat of a self-portrait of Stuart Freeborn.)
It was actually only after The Phantom Menace that Yoda became a complete CGI character:
In The Phantom Menace, he was redesigned to look younger. He was computer-generated for two distant shots, but remained mostly a puppet. The puppet was re-designed by Nick Dudman from Stuart Freeborn's original design.
For the remaining two episodes of the 20th century sextology, his CGI appearance, however more dynamic, was still dictated partially by his puppet physics:
His performance was deliberately designed to be consistent with the limitations of the puppet version.