Gather all your ingredients and utensils.
You will need a medium-sized mixing bowl and a whisk.
Add mayonnaise, ketchup, mustard, horseradish, Worcestershire sauce, garlic powder, salt, and black pepper into the bowl.
Whisk these ingredients together until they are completely combined.
Make sure the mixture is smooth and creamy.
Stir in the chopped celery, green bell pepper, and red onion.
Mix well to distribute the vegetables evenly.
Cover the bowl with plastic wrap and refrigerate for at least 1 hour.
This chilling time enhances the flavors!