The Karl-Thing was a Thing which assumed the form of Karl, a geologist stationed at Thule Station. While not used in the theatrical version of the film, the creature can be seen in a deleted scene from the 2011 film The Thing.
After the Juiliette-Thing rampages through the Norwegian station, killing and partially assimilating Karl, the crew torches the beast and goes back to check on the geologist's corpse. They discover that he is gone and follow a blood trail to a nearby office. Entering the room, they see a partially-finished Karl-Thing emerging from behind the desk. The chest wound he sustained is gone and his skin is unnaturally lined with veins. Seeing the others, he lets out an inhuman roar before being incinerated.