In China they use the word "Sifu"—it is a very special word indeed. Although it is always pronounced the same way its meaning differs depending on who is saying it.
The first spelling, 師傅, is the more generic, albeit weighty, use. It means 'master' and can apply to anyone who has mastered a trade. It is a sign of reverence for the time and energy someone has put into studying and working in a craft.
The second spelling, 師父, is far more personal. It holds the dual meaning of teacher and father. It represents the bond between a master and a student and transcends the first meaning. Even if someone sees your Sifu as a master of his trade this represents something deeper between the two of you.
This is also true in advertising.
There are masters: Bernbach, Lois, Hegarty, Abbott, Ogilvy, McCabe, Gossage, Wells, Burnett, Trott, Sullivan and a multitude of others, who represent the best of the trade. They leave behind information that enriches the generations after them. They are also generally revered by those starting out and practicing the trade. When we aspire we aspire to be like them—to do work that leaves an impact on culture and the industry.
Then there are the teachers. The people you strive to work for. The people who leave such an indelible mark on you that you cannot help but feel indebted to them.
One example of this I have seen recently is Eric Kallman (CW on Old Spice, now BFG9000) and Gerry Graf. According to Graf's blog Kallman has called him "boss" since they first worked together. Even when they weren't working together that was the term he used. I think there is a certain insecurity that all creatives have where they are looking for someone to help forge their path/ find a solid direction.
So thinking about who your Sifu may be, or who you want it to be, might be a good idea. You never know who will change the direction of your life.
I have been tremendously lucky to meet and work with the people I already have. Without them I wouldn't be nearly as motivated or eager to work towards something great every day. If any of you are reading this thank you very much.