Many believe that being a theif requires absoute solidarity. But contrary to that belief, there are many people scattered throughtout skyrim to help you through your journey of becoming a master thief. Everyone ranging from beggars to jarls have a side to them that they hope no one knows about. It's our job to know that side, and bring it out to benefit oursleves.
Brynjolf is the main face of the Thieves Guild. He will be the first one of the lot that you meet and he will be your ticket it. Without the Thieves Guild, it will be mighty difficult to gain the favor of the other people on this list. Brynjolf is the key to your success.
Tonilia is the Thieves Guild resident fence. She is found hanging around the Raggod Flagon and is willing to buy and sell anything. She doesnt care if you found it in a cave or in someones pocket. If it's worth anything, she'll buy it from you. All while giving you the appropriate amount of sass.
If you are ever wondering where to go, or what to get done, than Vex and Delvin are the people to go to. They handle all of the clients who want to utilize the Thieves Guild's services. You, of course, are free to do as you please, but doing a job for them once in a while may reduce the sarcasm level for the time being.
Maven may be difficult to please, but if you are friends with her, you are friends with the world. For the very few that have made her happy, she is willing to go to great lengths to help you out. She is on a different level than the usual thief-probably because she never does the thieving herself. Her nobility will become very beneficial for you. If you are ever wondering where to go, or what to get done, than Vex and Delvin are the people to go to. They handle all of the clients who want to utilize the Thieves Guild's services. You, of course, are free to do as you please, but doing a job for them once in a while may reduce the sarcasm level for the time being.