He was voiced by Harry Shearer.
Wainwright Montgomery Burns was the father of Clifford Burns and grandfather of Charles Montgomery Burns. Wainwright forcibly adopted him and is responsible for transforming from a carefree boy into the miserly old man he is now so often perceived as. Many of Charles Montgomery's cold-hearted characteristics are noticeable in Wainwright as well.
He was a racist, villainous man who owned a large plantation in the 1860s and owned a slave named Virgil who is directly related to Homer Simpson and his family.
Around 1891, Wainwright was the same mysterious figure who lured youn Charles away from his loving parents to adopt as his own son, intending to corrupt the young boy to be like himself: caring only about greed and power. Before this time, it seems, young Charles was so lighthearted and pleasant that his parents even gave him the pet name "Happy".
It has been referenced that Wainwright directly destroyed Charles Montgomery's innocence (it may even have been Wainwright who gave Charles his own middle name "Montgomery" in the first place).
In 1909, Wainwright took his grandson on a tour of his atom smashing factory, where he had an atom smasher who was trying to steal atoms taken away, probably to be beaten up.
It has been theorized that Wainwright owned stock in "Confederated Slaveholdings", which he passed on to his grandson by 1997. This would make sense, since Wainwright was an adult during the 1860s, during the Civil War.
- Wainwright Montgomery Burns - The Simpsons Wiki