He is a parody of the Legend of Zelda's Link, that behaves similar to a player stereotype of performing side quests over the main objective. Lunk's power is practically limitless, as without the tranquilizers and muscle relaxants in his Lunky Chunks, he becomes large eneough to break the Earth in half and use the moon as a spoon to eat the Earth's core.
Lunk's name is a mesh between the name "Link," and the word "Hunk" which is usually to describe someone who is largely muscular.
It could also simply be a corruption of "Link" or a play on the word "Lunkhead" which means someone strong, but stupid.
The reason why Lunk look buff is due to him drinking goat milk all the time as a child. and it's the reason why he is out on a adventure, so his dad can sell the milk instead of his son drinking the milk.