Gothir is a nation of people on the western coast of the Drenai world. Their lands are located to the north west of the Drenai lands and they border the Nadir Steppes. Its capital (pre-Nadir conquest) is Gulgothir, New Gulgothir being the post-conquest capital.
In The Legend of Deathwalker is the only real indepth look at the political situation in Gothir and it shows that the Mad God-King was kept in power only because the nobles and religious leaders were held in check by the Guard.
From what little is available on their culture, it appears - like Ventria - that they take aspects from many Middle-Eastern empires with a little bit of Roman thrown in. They are ruled by a God-King - Egypt - and at one point take enemy hostages from the Nadir to turn them into Janissaries (slave soldiers) - Ottoman Empire - and the God-King appears to only be in power for as long as he has the support of the Royal Guard (much like the Roman Emperors and the Praetorians). They seem to be much like the Drenai, physically speaking, going from the few descriptions available.
The people who would eventually become the Gothir were a peaceful people who once occupied an area which covered from their later location on the north-west coast down through the lands of the eventual Drenai nation. They were displaced from the latter by the nomadic people who would become the Drenai.
After the Nadir arrive in the steppes, they begin attacking the Gothir, forcing them to become more organised and fortify their settlements. When the Nadir tribes fragmented and started fighting each other, the Gothir were able to dominate them and begin to pay them back for the years of raids. Their hatred led them to brutalise the Nadir and over the centuries they viewed the tribes as lower than animals, often making raids on them just to abduct men for the mines or for some nobleman's hunting entertainment.
It was centuries of this that would lead to the Gothir being one of Ulric's first conquests after unifying the tribes.