He is the grumpy next-door neighbor of the Loud Family and he seems to get along well with them. After "11 Louds a Leapin'", he and Lincoln became friends. Like the Louds, he also has a big family, but lives alone, far from them.
He first appears in the episode "Chore and Peace", but his name wasn't revealed until "A Tattler's Tale". Not much is known about his past, but it is revealed that when he was a child, his hair was brown, and he still wore glasses.
In the episode "Lock 'n' Loud", it is revealed that he's allergic to walnuts.
Bud Grouse is the typical grumpy old man of the neighborhood.
He doesn't like to see objects from the other neighbors in his yard, so he decides to keep them in his house, and doesn't give them back. He can get upset by the Loud family's constant noise and messes.
He is usually unhelpful when the Louds ask him for a favor. He agrees to help only when he gets food in return like lasagna or muffins.
It appears that whenever the Louds (possibly anyone) involve him in a plan, he'd usually explain the plan out when something goes wrong, as seen in "Lock 'n' Loud", when he said next time if he was going to pretend to be robbed, the muffins should not have walnuts, and in "Garage Banned", he also accidentally said that he crashed into his own garage instead of the Louds' garage.
Despite his grouchiness, it was shown that in "11 Louds a Leapin'" that he can be sincere and kind to others and that his grumpiness might stem from envy toward the Loud family, due to him not being able to visit his own family, which is just as big as the Loud family.
Bud Grouse is a heavy elderly man. He doesn't have hair (except for the two hair strands that he has on his head), he also has a white mustache.
He wears a white shirt under a black waistcoat, a blue tie with dark lines, brown pants, and dark brown shoes. He also has a golden pocket watch in his waistcoat's right pocket, and a pair of little glasses.
He was simply referred to as "Neighbor" in the end credits from his debut episode until "A Tattler's Tale".
The word "grouse" means "complain" or "grumble", which matches with his personality, as seen in "11 Louds a Leapin'".
It's revealed in "11 Louds a Leapin'", that Mr. Grouse also has a large family, just like the Louds.
In the same episode, he calls Lincoln by his name for the first time, instead of the usual name Loud.
This episode also reveals that until the events of the episode, he'd get even grumpier than usual around Christmas due to missing his family.
In "11 Louds a Leapin'", he owns a Fearsome Flyer 1000 when he was a young boy, which he gives it to Lincoln as a Christmas gift, to make up for destroying his previous sled.
He got a redesign in "A Tattler's Tale".
In "Chore and Peace" and "A Novel Idea", his eyebrows are black instead of white, his head is shaped differently, has no single strand of hair hanging from his head, and lacks a golden pocket watch.