Ludwig von Koopa

Ludwig is Papa Smurf's right hand Koopa, and is the oldest Koopaling

The Smurfs Meet the Mario Bros.
Ludwig's debut was in this episode. He started out as a bad guy, but ended up being a good guy. He always shouted "Stay on topic!", and has been doing that ever since.

The Smurfs Meet Greg Heffley
Ludwig has an even bigger role than in his previous appearance. He shouted "Stay on topic!" during all of the off-topic paragraphs.

The Smurfs Meet Percy Jackson and Annabeth Chase
Ludwig has the same role as he did in The Smurfs Meet Greg Heffley. He always shouted "Stay on topic!" during all of the off topic paragraphs. He also commented on when Percy and Annabeth made their relationship official.

The Smurfs Meet Captain Underpants
Ludwig has to control more than one off-topic paragraph this time around. Now we can see that, like most of the Smurfs, that he likes Smurfette. As usual, Ludwig shouts "Stay on topic!" every time there is an off-topic paragraph.

The Smurfs Meet the Real World Kids
By now, Ludwig has been promoted to Papa Smurf's right hand Koopa. He still shouts "Stay on topic!" whenever he sees an off-topic paragraph, but when the podoboos ate the NES, Ludwig shouted a bunch of bad words, making the narrator suggest that Ludwig was getting tired of shouting "Stay on topic!"

The Smurfs and Friends: The Movie
Ludwig is one of the few Smurfs Meet characters that go to New York City. He helps Papa Smurf with almost everything, and kicks Patrick in the face. His catchphrase in this movie is "Aie, yaie, yaie!" He also shouts "Stay on topic!"

The Purple Smurfs
Ludwig is trying to cut a log with his eyes closed, but the bridge collapses. He is also one of the last Smurfs Meet characters to get bitten. This is the first episode where he does not shout "Stay on topic!"

The Smurfette
When Smurfette admits what she has done, Ludwig, who always has trouble talking around pretty girls, stammers something like "My Smurf is worse than my bite. I mean....."

Jokey's Medicine
Ludwig is one of the Smurfs Meet characters to get "surprised" by Jokey. He, Greg, George, Harold, Percy, Annabeth, Roy, and Iggy plant to show Jokey how THEY feel when Jokey's surprises them.

A Hug For Grouchy
Ludwig, along with Percy, Annabeth, and Smurfette try to convine Grouchy that there's more to life than being Grouchy all of the time.

King Smurf
Ludwig is one of the "rebel Smurfs" in this episode.

The Astrosmurf
It was Ludwig's idea to make Dreamy think he was on the moon.

April Smurfs Day
Ludwig (aside from Brainy and Grouchy) is the only one who hates April Smurfs Day.

Happy Valensmurfs Day
Ludwig said he really doesn't like Valensmurfs Day, so Smurfette, Clumsy, Roy, Iggy, and Rowley try to cheer him up.

The Smurfs and Friends: A Christmas Carol
Ludwig and Brainy were the Smurfs of Christmas Present in this episode. Ludwig is also a fan of fruitcake (without the actual fruit).

The Great Smurf War
Ludwig is the Smurf who leads all of the Smurfs into battle in this episode.

The Smurfiad
Ludwig has the same role as Achilles, except for two things: He doesn't die, and he is shown in the wooden horse.

The Smurfs and the Characters from Other Stories
Ludwig is the best man at Percy and Annabeth's wedding. He also becomes great friends with Tyson, Nico Di Angelo, Chirag Gupta, Rachel Elizabeth Dare, and Tryclyde.

The Koopalings' Christmas
Ludwig, Lemmy, Roy, Iggy, Wendy, Morton, Larry, and Bowser Jr are the main characters in this one. They (accidentally) wish it was Christmas every day, and get some really BIG surprises!

The Final Battle
Based on the Norse myth Ragnarok, Ludwig takes on the role of Thor. UNLIKE Ragnarok, it has a happy ending. The Smurfs and their friends don't die, the world wasn't destroyed, and they all lived happily ever after. Ludwig hits Azrael in the head with Thor's hammer.