Uggard is Ruffnut and Tuffnut's uncle, mentioned in the episode "Ruff Transition".
|| Come on, Ruff, remember when we picked the fleas out of Uncle Uggard's back hair? And then you got fleas because of it? [src]
|| — Tuffnut
When Ruffnut has difficulties washing Wingnut, Tuffnut reminds her of the time when they helped their uncle Uggard get rid of fleas. After the experience, Ruffnut also got infected with fleas.