Keldar was the father of Quark and Rom and husband of Ishka, a Ferengi whom Quark remembers as a model businessman but who in truth had little talent for profit.
Keldar has died by the time of the series and is discussed in the third-season episode Family Business, when Quark returns to Ferenginar to deal with his mother's illegal earning of profit.
Quark has always idolised his father and blames Ishka's unconventional ways for the family's modest means. Rom and Ishka set him straight: Keldar was a kind husband and father but a poor judge of an opportunity, and it was Ishka who understood business. Had he listened to her advice, she says, the family would have prospered.
Rom adds that Quark takes after their mother in his head for finance, an observation Quark finds hard to accept. Keldar's memory is invoked again in later Ferengi episodes, usually by a son who would rather not hear the full story.