Mr. Henderson is a character who resembles Captain K'nuckles except with a mustache and fancy clothes which has proven rather unfortunate for him because of his resemblance to K'nuckles. This has gotten him into trouble a lot.
In "Come Home Cap'n", he had the misfortune of visiting Bubbie right after she kicked K'nuckles out. He walked up to her and said "Evening whale. I would like to live in your mouth". Bubbie responded by telling him "Nice try, K'nuckles. I know it's you". She assumed it was K'nuckles trying to sneak back into her mouth. He, however, having no idea who K'nuckles was, replied "K'nuckles who's K'nuckles?" He introduced himself as Mr. Henderson however, Bubbie, still believing it was K'nuckles trying to sneak back in, she beats him up and kicked onto Stormalong. K'nuckles walked by and gasped at his resemblance to him, but he was quickly distracted by a man with a crevatte and ran off.
In "Lead 'Em and Weep" Flapjack and K'nuckles gives a guy a wedgie and was about to kill them but Bubbie saves them and put Mr. Henderson and his assistance Bobby in their place, then they were the ones who got hit by the enraged man. After this, they were never to be seen since.