A senior figure or leader in one's field.
Example:
After dinner the guest of honor, a nestor among journalists, shared some of his wisdom with the other guests.
Nestor was another character from the Iliad, the eldest of the Greek leaders at Troy. He was noted for his wisdom and his talkativeness, both of which increased as he aged. These days a nestor need not go on at such length; he may share his knowledge or give advice with few words.