Tsang Wuqiong, the August Emperor of Jade, the Infinite King
Some sovereigns prefer a different sort of tax from their subjects - whether freely given, or taken by force.
Real World: some Indians in the Amazon treat their eyes with a traditional potion applied with palm leaves. Brutally painful, the drug alters vision, giving the jungle's dense green walls greater texture and dimension. You could adapt this to desert or swamps, or other hard to navigate regions.