Kermit Bryce Eller, who is 6′ 5″, made appearances in the suit promoting Star Wars and even appeared in a different, earlier Vader suit for the 1978 Academy Awards.
Kermit Bryce Eller stopped appearing as Darth Vader around 1982, stating the popularity had worn off a bit by then.
If you have around $1 million to spend, you can bid on an incredibly rare Darth Vader suit, which was made around the time of The Empire Strikes Back.
The Darth Vader suit is movie quality and may have been used in The Empire Strikes Back, but it has been in a Thousand Oaks, California storage unit for nearly 40 years.