Romans could be either patrons or clients, a social stratification that proved mutually beneficial.
The number of clients and sometimes the status of clients conferred prestige on the patron. The client owed his vote to the patron. The patron protected the client and his family, gave legal advice, and helped the clients financially or in other ways.
A patron could have a patron of his own; therefore, a client, could have his own clients, but when two high status Romans had a relationship of mutual benefit, they were likely to choose the label amicus ('friend') to describe the relationship since amicus did not imply stratification.
When slaves were manumitted, the liberti ('freedmen') automatically became clients of their former owners and were obligated to work for them in some capacity.
There was also patronage in the arts where a patron provided the wherewithal to allow the artist to create in comfort. The work of art or book would be dedicated to the patron.
Marius said that once a man reached the curule rank (dictator, consul, interrex, praetor, magister equitum, or curule aedile), he could no longer be a client. ("Review of Personal Patronage under the Early Empire, by Richard P. Saller," by A. N. Sherwin-White. The Classical Review, Vol. 33, No. 2. (1983), pp. 271-273.)
Examples: We know very little about Juvenal (whose 7th satire gives a look at the benefits a good imperial patron confers on a poet), but since he didn't dedicate his work, Juvenal probably didn't have a patron, and so may have been independently wealthy.