Whiterun is a large city in central Skyrim, and the capital of Whiterun Hold. Its location means that it is an important trading hub. The Companions, Skyrim's guild of fighters, make their home in Jorrvaskr, which is located in Whiterun's Cloud District, next to the Skyforge.
Jarl Balgruuf is officially aligned with the Empire, but he is noncommittal until Ulfric forces his hand and he fully sides with the Imperial Legion. He is an important figure in the Main Quest, sending the Dragonborn to Bleak Falls Barrow to learn his first shout, to the Western Watchtower to slay his first dragon, and to High Hrothgar to learn the draconic language from the Greybeards.