Prior to Star Trek: Deep Space Nine, the Ferengi race weren’t well regarded.
When the Star Trek: The Next Generation series was launched, the Ferengi were intended to be that series’ new baddies much like the Klingons were for Star Trek: The Original Series. However, their portrayal on that series didn’t do the race a whole lot of favors. The Ferengi were regarded as being quite inept, primitive, and only interested in greed & lust.
When DS9 started, the Ferengi were largely still regarded as such, but a number of other redeeming qualities were bestowed upon specifically the Quark character. Later on, his brother Rom began showing some technical know-how and became the reason that the Dominion couldn’t get their reinforcements through the Bajoran wormhole.
Rom’s son Nog showed the most growth as a character over the course of the 7-year series, as he started the series essentially as a juvenile delinquent who got himself & the Station Commander’s son, Jake Sisko in trouble with security quite often.
By season 3, Nog had grown so much as a character that he desired to become the first Ferengi to attend Starfleet Academy and become a Starfleet Officer. He saw that as a Ferengi, he “didn’t have the lobes” for business and wanted more out of life than what he had seen of his father’s life.
For the first time in all of the previously seen Star Trek series, DS9 took us to Ferenginar and further explored what it was to be a Ferengi through stories including Quark, Rom & Nog’s family, the Ferengi Commerce Authority and the Grand Nagus. The writers of Star Trek: Deep Space Nine did a wonderful job of rehabbing a race that the writers of TNG let go by the wayside.