Thank Nick.
That is what we call a POSK; a kamado type cooker that Richard Johnson made back in the day out of concrete and chicken wire.
It is not a Dennis Komodo Kamado.
That threaded rod is probably totally rusted to the spider collar in the top.
You may have to resort to a rusted bolt approach, i.e. liquid wrench. bear in mind to cover all the concrete surfaces so as to avoid them absorbing the liquid.
Others may have suggestions.