This is a rather philosophical question, I think. We incorporate values from various points within our culture - from our families, our schools, and from our communities at large (including the media).
Bosses, teachers, parents and mentors can be as influential as friends and probably moreso if we look at professional ethics in particular. If we are looking at our ethical systems on the whole, we run into the "individual" problem because everyone has a different set of experiences from which they draw lessons of values.
I would argue that all philosophies and concepts that a person knows or has studied to some extent shape that person. Of course, those thoughts that the person has embraced shape that person the most. But I would also argue that even if a person does not embrace something, as long as there is exposure, there is influence. For example, if a person rejects something vehemently, then that very thing has caused a reaction in that person. That person, therefore, has been influenced to some extend.
I would also say that the society in general also influences a person. What influences a person the most is probably society, in fact. So, it is also important to know what philosophies and concepts have shaped that culture or society.
Finally, all of these influences shape what a person deems wrong and right. A person's ethics is forged in this context.