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Although we see Ferengi from the beginning of TNG, Quark as a main character represents an opportunity to dive much deeper into the race and their background and traditions. Of course, his black market ways often draw the ire of station security constable Odo, as evidenced in this counterplay in the episode Profit and Loss.
QUOTE (from Profit and Loss, S2):
Odo: I heard an interesting rumour today.
Quark: Only one? I started at least twelve.
...
Quark: I never told you this, Odo, but I consider you as dear to me as my brother.
Odo: [laughs contemptuously] I've seen how well you treat him.
Quark and his brother Rom end up in many silly adventures together, like when they travel back in time to 1947 Earth when trying to drop off Nog at Starfleet Academy in the episode Little Green Men.
QUOTE (from Little Green Men. S4):
Quark: What's that disgusting smell?
Nog: I think it's called tobacco. It's a deadly drug. When used frequently, it destroys the internal organs.
Quark: If it's so deadly, then why do they use it?
Nog: It's also highly addictive.
Rom: How do they get their hands on it?
Nog: They buy it in stores.
Quark: [stunned] They buy? If they buy poison they'll buy anything. I think I'm gonna like it here.
Quark's best customer is Morn, who never is seen speaking on screen. Although the best Morn episode is definitely Who Mourns For Morn, Quark expresses his gratitude for his best customer on many occasions, such as in this clip from the episode The House of Quark.
QUOTE (from The House of Quark, S3):
Quark: Now I know we're doomed.
Rom: Why, brother?
Quark: Rule of Acquisition 286: When Morn leaves, it's all over.
Rom: There is no such rule.
Quark: There should be.
Even though the latter seasons of DS9 grow darker thanks to the Dominion War, Quark's personal stories always bring levity thanks to things like the Grand Nagus becoming romantically involved with Quark's mother. In the episode Ferengi Love Songs, Quark is able to push off the pesky investigations of Brunt, a Ferengi Commerce Authority liquidator who is always trying to bring Quark down for infractions against Ferengi practices, thanks to the help of the Nagus.
QUOTE (from Ferengi Love Songs, S5)
Quark: What are you doing in my closet?
Brunt: Conducting official FCA business.
Quark: In my closet?
...
Brunt: I want you back in business. It gives me an opportunity to keep my eye on you, because one day you are going to make a mistake, and on that day, you're going to lose more than your license!
Quark: But that day is not today. Now, back in the closet, where you belong.
Quark was played by Armin Shimerman, who is also known for roles as Principal Snyder on Buffy the Vampire Slayer, and as Andrew Ryan in the Bioshock video games. Despite coming up on his 70th birthday, Shimerman still acts and does voice work today.
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