According to "House Music", he tried to play in a music band, but his bandmates kicked him out, because they did not like his cowbell playing.
According to "L is for Love", he and Rita met when he was walking through the street and they fell in love at first sight.
Lynn Sr. wanted to be a chef, but to keep his wife and children fed and well, he worked as an IT specialist.
Lynn Sr. is stern, and often calls a halt to his kids' fights, but he loves and cares about them. He also loves his wife, and often acts playfully romantic towards her. He has been shown to have a childlike side at times, even sometimes taking part in his kids' antics, when it's all in good fun. He's also the more sensitive of the two parents, often necessitating his wife, and stepping in whenever he needs to pull himself together.
He is also shown to be quite neurotic; as he screams and faints at the sight, sound, and idea of spiders, as well as Lana's mud wrestling, horror movies, and Halloween.
He has a habit of prefixing words with "ding-dang" when frustrated.
Lynn Sr. wears a sea green sweater over a light green checkered collar and cuffs, brown slacks and shoes. He has a long pointy nose, brown eyebrows, and curly brown hair that is thinning on the top.
In "House Music", when he is playing the cowbell, he wears a yellow-striped shirt, and green pants with a rip that exposes his underwear. In his youth, he sported a mustache, though he seems to have shaved it by the time he met Rita. His hair was also straighter and parted in the middle.
Lynn Sr.'s entire face was never shown during the first season. His face was revealed along with Rita's face in the Season 2 premiere.
He believes singing while cooking improves his cooking, but it took him years to perfect his "cooking ditties". In addition, he sometimes sings while doing activities unrelated to cooking, such as checking the mail and changing Lily's diaper.
He has a tendency to lose consciousness when he is afraid. For instance, he spent most of Halloween unconscious due to his fear of the holiday, and almost delivered Lincoln but he passed out before he was able.
He is "sensitive" to raised voices, and if he would pick a superpower, it would be flight.
In the Polish dub, his name is Henryk, and he is the senior of Lana (Henryka) instead of Lynn Jr (Helena).
Sometimes fear renders him unable to speak coherently, but Rita understands him nonetheless.
The first dish he ever served someone else was linguini with clams, which he calls "Lynn-guini", and which is apparently famous among his family.
Lynn Loud SR's Wildest Food Dishes! The Loud House