As you successfully complete contracts for Duke, or any other agent, you will gain standing. You can lose standing by failing or declining contracts. By successfully completing many contracts, the difficulty level, rewards and amount of contracts available will begin to rise.
If you decline a contract you will lose less standing in comparison to when you fail a mission. So don't just accept your contracts willy nilly!
Upon first meeting a contract giver / mission agent, everyone will start on Easy difficulty. As an example with Duke, The targets and challenges you face will be very simple and the rewards will be low - this will change dramatically as difficulty increases. In contrast, some Expert contracts may be impossible to complete without assistance from others, but they'll provide on average 16x higher money rewards and 5x mission credit rewards.
You can increase the difficulty of contracts he provides by increasing your standing with him. There are 5 levels of difficulty: Easy, Medium, Hard, Very hard and Expert. Each tier dramatically increases the money and mission credit reward, and will unlock more contracts that were previously unavailable.
Before you can unlock a new difficulty level, Duke will provide a special contract that you must complete. By completing these special contracts, future contracts will have a chance to spawn at a higher difficulty. Some specific contracts have set difficulty levels, so you may sometimes receive lower difficulty contracts than you're expecting.
The mission credits panel (seen at the bottom of the missions page) is where you can spend your mission credits. Mission credits are a new currency given when missions and contracts are completed.
Six random rewards will spawn here at a time. When one is purchased, it will be replaced by another one. Every unpurchased reward will be replaced by a new one every 7 days.
The rewards may appear expensive at first due to the amount of mission credits received at lower difficulties. The team behind Torn also wants the special rewards to actually be special - by keeping their prices high.
George gives new players introductionary missions to get them going in the game, more information about these missions can be found Here.
Anonymous is a mission giver which will introduce you to all the mission agents. Currently he only has one mission, which is an introductionary mission for Duke, which requires you to complete 10 contracts, You will gain an honour bar and 100 mission credits for doing this.
Anonymous will be unlocked at level 5
Duke, The Loan Shark, Is a mission giver who will ask you to complete contracts in return for mission credits.
Contracts are like mini-missions. You'll be asked to complete fairly simple randomly generated tasks that utilize already existing game mechanics. Duke currently provides 67 separate contracts of which most are repeatable, we'll also constantly be adding new ones based on feedback and suggestions.
Every agent we add will have a different theme. Duke's contracts are almost entirely focused around attacking (a sensible starting point), so most of the tasks will be somewhat similar--although receiving the same contract with the same task and target more than once is very rare.
Duke will provide one contract per day, at midnight. You can have up to three available or in-progress contracts at a time.
Professor Amanda Ravenscroft, a mission giver that has yet to be released.
As of now there is no information about agents after Amanda, but there surely will more.