In the mid to late-seventies, Eastern Airlines, which had for some years been keeping informal track of its best customers, very quietly instituted a level known as "Executive Traveler" for these customers. This came with a brown suede ticket holder and a brown card on which your membership number was stamped (it was really your phone number).
The Executive Traveler never sat in coach when there was a first-class seat available (on a standby basis) and always got some sort of seat even if the flights were completely sold out. I have vivid memories of being personally escorted through crowds of people trying to get on to flights at various airports when there were extensive weather or other delays and cancellations. Even after the institution of the formal Frequent Traveler program in the early 80's, The ET designation survived until Eastern's demise in 89.
To this day, if you hear a CO agent refer to an Elite flyer as an ET, you know that this is a former Eastern employee who had been absorbed into Continental at the Lorenzo takeover.