Zek was the Grand Nagus of the Ferengi Alliance throughout most of the 24th century.

Zek was an aficionado of Hupyrian beetle snuff. Liberal minded he seemed not to worry about clothed females as long as it was in the home not in public.

In 2369, he suddenly announced his new successor, Quark and apparently died soon after. It was discovered that this was only a ploy to test his son Krax’s worthiness for the position. However, Krax did not succeed as expected, and Zek had to postpone his retirement.
(DS9: "The Nagus")

In 2370, Zek attempted to open negotiations with the Dominion, and although he opened contact with the Karemma and the Dosi for tulaberry wine, he was unable to contact the Dominion.

(DS9: "Rules of Acquisition")

In 2371, Zek appointed Quark as his representative to accompany the USS Defiant on its mission to make contact with the Founders of the Dominion, through Benjamin Sisko.
(DS9: "The Search, Part I")

As Grand Nagus, Zek had the power to appoint a Grand Proxy to speak on his behalf.
(VOY: "False Profits")

Zek would later ask Quark to remind Sisko of his instrumental role in the events leading upto first contact with the Dominion, after his nephew Belongo, was detained by authorities on Aldebaron III. Sisko said he would look into the matter, but made no promises.
(DS9: "Past Tense, Part I")

Later that year Zek came into possession of a Bajoran orb, and attempted to contact the Prophets to ask them to reveal the future to him for financial gain. Finding Zek's greed offensive, the Prophets returned him to Deep Space 9 after reverting him to a point in Ferengi evolution when the species was less profit-driven. Zek then promptly created the Ferengi Benevolent Association to provide aide to poorer worlds, devised new Rules of Acquisition that emphasized giving, and offered to give his orb to the Bajoran people for free. Quark quickly discovered that Zek had been altered by the Prophets, and convinced them to restore Zek to his former self. Zek then cancelled all of his reforms.
(DS9: "Prophet Motive")

When someone (later revealed to be Brunt) pre-bought his vacuum desiccated remains, Quark thought that it was Zek.
(DS9: "Body Parts")

In later years Zek began to experience a dramatic change in his policies. In 2373 he fell in love with Ishka, Quark’s mother and a radical feminist who became the "power behind the throne." He eventually amended the Ferengi Bill of Opportunities to allow females the right to wear clothing. Few accepted this radical change at first, and Zek was ousted by Ferengi Commerce Authority in the form of Liquidator Brunt (who wanted to be Grand Nagus). However, he was able to convince a few influential FCA commissioners that females represented an unexploited business opportunity, and Zek was reinstated.
(DS9: "Ferengi Love Songs", "Profit and Lace")

In early 2374, Zek offered to buy Rom's freedom from the Dominion.
(DS9: "Favor the Bold")

Despite the Ferengi Alliance's official neutrality during the Dominion War, Zek maintained close relations with the Federation, and periodically requested status reports about the course of the war. In late-2374, Nog and Jake Sisko were on their way to Ferenginar, where Nog was to meet with Zek on behalf of the Federation, when their Runabout was ambushed by the Jem'Hadar.
(DS9: "Valiant")

When Ishka was captured by Dominion forces while returning from a trip to Vulcan, Zek commanded that Quark put together a team of mercenaries to rescue her.
(DS9: "The Magnificent Ferengi")

Zek sent Quark on another fact-finding mission to the front lines in the Chin'toka system in 2375.
(DS9: "The Siege of AR-558")

Shortly thereafter, Zek and Maihar'du (Zek's Hupyrian personal assistant) crossed over to the mirror universe hoping to make some profit. However, they were captured by the Alliance. Quark and Rom rescued them, by bringing Regent Worf a cloaking device.
(DS9: "The Emperor's New Cloak")

Later that year, Zek finally retired just after implementing new social welfare programs, appointing Rom as Grand Nagus, and passing to him the Grand Nagus' staff as a symbol of his new office.
(DS9: "The Dogs of War")