If you're a fan of horseradish, you'd be surprised at how easy this is to make from scratch. And you have the ability to control the intensity level.
1 lb horseradish root
1-1/4 cups distilled white vinegar
1-1/2 tsp salt
1/2 tsp sugar
Peel the horseradish root and chop into 1/4" to 1/2" chunks.
In a well-ventilated area, preferably outside, process the chopped horseradish root until desired consistency. If you want milder horseradish, add the remaining ingredients before you start processing. If you like it more intense, wait several minutes before adding the remaining ingredients. The longer you wait, the more kick you'll have. Process again to combine.
Very carefully remove the lid and taste. Adjust salt/sugar and reprocess if needed.
Transfer to glass jars for storage. Should keep for about a month in your fridge.