Lifetime member
I still have my (and use it at MSP) the Lifetime membership I bought way back in the ?? maybe 80's.
As I remember it cost $500 and was 'Grandfathered' when Delta took over Northwest. Delta does not offer 'Lifetime memberships'
Prior to having to BUY a membership there use to be a "Frequent Flyer Club" membership that was FREE to anyone that flew a lot back around the 70's.
I still show it sometimes at MSP just to get a laugh from the 'OLD' crew that are still around, which is not many now days.