What was the word used to describe wealthy men in ancient Rome who sponsored people?

The word you’re looking for is _patronus_ (plural: _patroni_).

In ancient Rome, a patronus was a wealthy, powerful man who supported and protected clients (_clientes_). This relationship was called _clientela_.

It wasn’t charity. It was a structured social system — part economic support, part political machine, part status display. The more clients you had, the more powerful you appeared.