Uncle Lou is an unseen character. He is the 98 year old great uncle of main characters Jonah Flenderson and Martin Anderson. Because characters of The Lenny Leggo Show do not age as the show progresses, he mysteriously remains age 98 throughout the series, except for the pilot episode, Unhappy Birthday Martin Anderson, where he is mentioned to be on the verge of turning 98, placing his age at 97: determined albeit a major verbal brawl between Harvey Duncan and Randy Stallone regarding his age, which becomes central to "Unhappy Birthday Martin Anderson"'s plot.
Uncle Lou has had Alzheimer's disease since he was 70 years old: it was first discovered by his great niece, whom Uncle Lou was visiting for the day, when Uncle Lou yelled from the downstairs bathroom "Do I pull, or do I push?!". However, Uncle Lou's condition has changed little over the decades, unlike most cases, where the condition gets progressively worse over 3 to 9 years, the life expectancy of one who has Alzheimer's disease. He is currently paying regular visits to labs for experimentation and examination, hopefully to one day provide answers that will lead to a cure to Alzheimer's disease.