It's like a root vegetable, but isn't.
Kohlrabi is a vegetable that tries to disguise itself as a root vegetable, but thanks to something wierd it sticks out of the ground with one long, giant root. Many Normies don't know this, this is why they only eat meat. You can use it's leaves to make Kohlrabi Chips that you can use to channel your inner Troll.
Kohlrabi was invented in Germany when Heinz Doofenshmirtz created, "The Root Veggie-inator" for a science fair, but he lost to a baking soda volcano. Enraged, Heinz Doofenshmirtz shot the kid with this invention, but since Cauliflower flavored Gum was stuck in his, "-inator" it turned him into a root vegetable that actually wasn't one, he named it, "Kohlrabi" in memory of Balloony as it sounds like Balloony.
Somewhere in around 2010 in the vegetable patch of the garden of Big and Small, the Gwelf, a malodorous organism created by the Dig-Its who wanted to thieve materials, resources and nourishment for their own benefit, was once caught trying to abscond with Big's latterly planted kohlrabi. The Gwelf had gotten away with this crime scot-free, as there was hardly any plausible evidence of the Gwelf's true occupancy; everybody assumes he's a myth after all.