This is a post from 2008, but I haven't found an answer to the original question in the thread. The question was about the French translation of this term in the Pharma context, not marketing, politics, publicity or advertizing.
I work in the Pharma industry and we use this term a lot in English, but I don't know what the French equivalent is. When we use the term KOL, we mean a physician who would be a prime expert in a particular therapeutic area in a certain country, someone whose opinion we can unconditionally trust when we are doing a feasibility of a new study, for example, and want to know if it's feasible in a certain country. Please help find a proper translation in French. Thanks in advance!