His owner, Karen Quigley, said the Chinese crested and Chihuahua mix died unexpectedly on Thanksgiving Day. She said Elwood had been dealing with some health issues but appeared to be doing well.
The dog was dark colored and hairless - save for a puff of white fur resembling a Mohawk on his head.
After winning the ugly dog title, Elwood became an online sensation. He was later the character of a children's book that promoted a message that it's OK to be different.
"He made people smile, he made them laugh and feel good. It was wonderful," said Quigley. "He will truly be missed."
The Associated Press contributed to this report.