It seems to me that this behavior may be a form of bullying. If it is, it is likely to continue until you resist.
In the past, I've been is a similar situation a couple times. What I've learned is this takes away from time you should be doing your job, and helps him do his. This helps him look better while making you look worse in the eyes of management. So, yes, be on your toes; generally, it's best to be cooperative, but don't spend too much time doing other peoples' jobs for them.
By taking direction from this person, you have shown that you will do his bidding, perhaps making him feel like he is your boss. This needs to stop, unless it turns out management sees you as subordinate to him, in which case you need to discuss what is really expected of you with your management.
There are a number of possible ways to respond. When dealing with him, remain professional and respectful. (Voice of experience: One of the times I had someone who wasn't my boss try to give me orders he started yelling at me when I said it wasn't my responsibility. After a little bit of his yelling I lost control and started yelling back. While I don't know what was said (if anything) to the other person, I was reprimanded for my behavior.)
One possibility: The next time he wants you to do something that's not really your responsibility say something like "Hey, I seem to be doing you a lot of favors, and thus far I've not needed them returned. How about you buy me lunch at my favorite restaurant." If his response to this is positive you get a free meal at your favorite restaurant! :-) During the lunch, you can have a conversation about why he needs all this help, and mention that it's not all in your area of work and want such requests to stop. Also you can talk about how you don't like how he says some things and would appreciate it if he made his requests more respectfully. You might also talk about the weather, sports, or whatever topic comes up that you two can discuss pleasantly. If his response to your request for lunch is negative, you can say "In that case, I've got enough to do and am tired of doing you favors. It's the secretary's (or IT's or whoever's) job to help you with this. If you really want my help, let's clear it with [YOUR MANAGER]." I suspect he won't want to go to management, but if he does, follow through, making sure to tell your manager that you've been doing several things for him that aren't in your area of responsibility. In whatever direction this goes, he should get the message that you're not willing to continue doing his bidding when it's not in your area of expertise.
Another approach is to just say you're busy and he'll have to get help elsewhere the next few times he asks you to do something. If he persists in asking these things, point out that he isn't your boss and you have other responsibilities. You might suggest that any time he wants your help in the future he should go through your boss. If he continues making these requests, have a talk with your manager about how this guy is trying to pull you into things that aren't your responsibility. Managers often like to see specifics when complaints like this are made, so it may prove useful to have some occurrences documented to back up to your claim. For example: On Monday he asked me to print his TPS report; on Tuesday he asked me to fix his printer; on Wednesday he asked me to staple 20 copies of spreadsheet S; on Thursday he wanted me to edit the document D he's working on.