Understanding why this person is putting pressure on you will help you find an effective way to deal with him. In most cases, people who make unreasonable demands do so for one of three reasons:
1. They're overloaded themselves
2. They're unaware of the impact of their demands and are therefore unrealistic about what you can do
3. They're just plain passing the buck.
It's possible that the Slave Driver is actually a slave to someone else who is piling on the work - the very work that is cascading down onto you. It may also be that the Slave Driver's ambition is pushing him to take on more than one person can reasonably handle. If the Slave Driver isn't able to fulfill his promises, the pressure may wind up on you.
A "clueless" Slave Driver may never have done your job and may not understand the time and energy it would take to produce results at the requested level. It is easy for people to make assumptions and hold unrealistic expectations. A clueless Slave Driver may not be aware of the other claims and constraints on your time.
Finally, some bosses simply consider it executive privilege to hand over their work to those below them. When you are asked to do both your own work and that of your boss, your job becomes nearly impossible. Bosses who pass the buck in this manner are the most difficult Slave Drivers to deal with.