Proventus Avenicci

Proventus Avenicci is the Jarl's advisor. Aside from asking for information about Whiterun, you can obtain a side quest to kill some random bandits, and buy a house in Whiterun for 5000 gold. He also is the one you go to in order to decorate your home.

He can usually be found standing next to the Jarl's throne, or in his bedroom in the back rooms of Dragonsreach.