Description: Grom would never follow anyone else, so if you take him he must be your General, regardless of the Leadership of any other characters. If you take Grom you must include at least one unit of common Goblins in your army.
In addition, Grom would never tolerate the presence of anybody who might threaten his command. Therefore you may not include any Orc, Savage Orc or Black Orc Lord characters if Grom is your General.