If you have a felony because of a robery can you become a us citizen?

It depends but it is possible. Is he even a resident?

No.

That depends what the sentence was and what year he did this.

He should be. However, it is a good idea to consult an attorney to make sure what actions may be necessary to take.

The answer to your question is probably. However, the answer to the inquiry really depends on where your friend was convicted, the definition of "robbery" in the jurisdiction where he was convicted and your boyfriend's immigration history (e.g. when did he become a resident, how did he become a resident, etc.). The best advice I can provide in a case such as this is to look for a reputable immigration attorney with familiarity on the immigration consequences of criminal convictions. This can e a complicated legal issue to resolve and I wouldn't take generalized advice indicating "don't worry" without having a full and informed explanation of why it will all be good. I would highly advise that your friend obtain advice on travel plans BEFORE leaving the US. Depending on when the conviction occurred, your friend could face significant potential consequences if he were to depart the US with a plan to return on his green card. While he will not be sported upon his return without having an opportunity to appear before an Immigration Judge, he needs to understand just what to expect before he leaves the US. I don't mean to scare you or your friend, but I cannot suggest with any more importance the need to follow up with a licensed and knowledgeable immigration attorney. There very well could be a resolution out there to what would appear to be a potentially large mess. Find a reputable person to assist, we are out there and we are very willing to help if we think we can do so and make it worth your time and expense. Be careful out there, lots of attorneys will ask for a lot and be far short on explanations. Make sue you understand what any attorney will be doing on your behalf BEFORE giving any money to anyone. Good luck.