Louis Kalhern "Grandpa" "Lou" Pickles (Born November 8, 1915) is the father of Drew and Stu, also the grandfather of Tommy, Dil, and Angelica. The elder patriarch of the Pickles family, young at heart, he likes to be adventurous. Occasionally, he flirts with women. He is commonly thought of as having a wild imagination from the many stories he tells of his earlier years. In these stories, the number 15 is prevalent in various ways. Whenever Lou appears, his usual routine is to fall asleep in the middle of telling the kids a story. He loves his grandchildren deeply and always enjoys spending time with Tommy. He shares a rivalry with his cousin Miriam. Besides his rivalry with Mim, he's had several other rivals. His bowling rival was Billy "Strike" Maxwell (seen in King Ten Pin), however Lou later regains his honor by beating him after its revealed that Maxwell was cheating the entire time. He also has a recurring rival with Conan McNulty, with Conan often lying to him and cheating.
When his wife Trixie has to go out of town, Lou takes care of his sons and grandchildren. And while he loves his sons, he has a great frustration with their constant bickering. Over the years, Lou has had many jobs, including a solider in the war, a cook, a repairman for small appliances, and a detective. Lou is also a bit of a schemer. He also has quite a talent for playing trumpet as he was given a solo for the war veterans concert in "Grandpa's Teeth". One of the things he loves to do is fishing and mostly watching TV, he's almost always seen watching a show involving fishing or watching TV for fun. While Lou enjoys doing new things, he can be very stubborn with trying some new things.
Lou Pickles has peach skin and a pair of white eyes with black pupils. He has gray hair and is often shown wearing a purple shirt and a green vest. He looks just like his son Drew Pickles when he was younger, but as he got older, he now looks more like his other son Stuart Pickles.
- Grandpa often talks about his brother Sparky Pickles.
- Grandpa usually uses the number 15 in his rants.
- In Aunt Miriam, Grandpa states he is actually 76 years old, meaning he could've been born in 1916. Grandpa's real age is unknown since he stated in the episode, Chuckie Get's Skunked, that he recalled a childhood memory with his brother Sparky back in 1906, meaning he was alive before 1916.
- In the pilot episode "Tommy Pickles and the Great White Thing", Lou is called "Stu Pickles Sr." in the credits.
- In Aunt Miriam, Miriam remembers that she and Grandpa played with their friends Bill and Jill when they were kids. Phil and Lil stated in Potty-Training Spike that Bill and Jill are the names of their aunt and uncle.
- In Touchdown Tommy, Lou stated that he played football at Minnesota State University.
- He is the only Rugrats character whose original voice actor died during the show's 14-year run; David Doyle died in 1997.
- In Wrestling Grandpa, Grandpa was a former wrestler known as "Pretzel Maker" Pickles.
- He needed to walk 15 miles to anywhere.
- His catchphrase is "And I needed to walk just about 15 miles there".
- Lou makes a cameo at the beginning of The Loud House episode "Linc or Swim", alongside several other elderly characters from past Nicktoons.