Comment by NickC25
Or you just get another loan from another party to pay the initial loan back.
Bezos probably has an army of banks, private lenders, and private capital connections to effectively have a lifetime of loans against his Amazon shares.
It's a pyramid scheme, except the guy at the top actually has the money and collateral.
These lenders will want some interest. The collateral is only useful if he defaults. If the collateral generates realized gains then those are taxed.