I just got this game the other day, and I've played up to the Montera area. I did all the quests and such so that I can go see the orc leader in the town, but then he wasn't in his throne room, or anywhere else for that matter. I checked with a friend who'd played this before and he said that the guy (I think his name was Varek?) was supposed to be in the throne room, so I'm thinking now that there is some sort of bug or something where he doesn't appear. Is there any way that I can fix this?
If you have already tried sleeping a night and then checking again in the morning if he is there, you could try to cheat via the console. It's the ~ key (the one under ESC and above TAB) that activates the console. Then you could try the following commands: "goto Varek" (make sure you get his name right… I can't remember his exact name at the moment either so you best check with your friend or with an online guide ) or "spawn Varek".
It might be that to be able to use the console at all, you might have to modify the ge3.ini in the Gothic 3 folder first. Open the ini file with a text editor and look for the entry TestMode=false . Change it from "false" to "true" and restart Gothic 3. Then try to bring down the console via the ~ key again.
If you have problems with the console (black box, unreadable text, flickering etc) then you could try to fix that by installing the 1.4 community patch.