From Monkey Island wiki
According to the waitress at Planet Threepwood on Jambalaya Island, Dwayne is the name of Guybrush Threepwood's father. However, she also claims that Guybrush is 6'4", has a big scar above his left eye and owns a big black parrot, so her information is untrustworthy. Guybrush himself never mentions his parents in Escape from Monkey Island.
Guybrush's father, who appears in Monkey Island 2 and its Special Edition, is slightly bald and wears black boots, a white shirt and brown trousers. He appears to be less talkative than Guybrush's mother. Also, in the Special Edition he is voiced by David W. Collins.