The Doctor has had many companions during the renewed series' run. Of all of them, several names stand out. Captain Jack Harkness is among them. Jack was charming, adventurous, funny, and flirty, and sacrificed his life to save the Doctor as well as other people. Of course, as all fans will know, Rose later brought Jack back to life and made him as close to immortal as they come.

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Jack's popularity among the fans was further proved by the fact he went on to headline his own show, Torchwood, where he led the team in Cardiff and investigated various alien threats. Captain Jack Harkness was always quick on his feet, and as such, came up with some truly memorable quotes.

5 Who Looks At A Screwdriver And Says "Oooh, This Could Be A Little More Sonic!"?

The Ninth Doctor uses his sonic screwdriver in Doctor Who

By the time Jack started traveling alongside the Ninth Doctor and Rose, he was already an experienced space adventurer who also traveled in time. As such, he wasn't as impressed by the Doctor's array of tricks and gadgets as Rose and other companions were.

When Jack met the Doctor for the first time, and they stood against the empty child and other enemies together, Jack was less than impressed by the fact that the Doctor decided to make a sonic screwdriver, instead of a sonic cannon, a sonic disrupter, or any other type of weapon. Of course, as Jack later realized, the Doctor was never about weapons. But Jack's sass and honesty were one of the character traits that made him so popular among the fans.

4 Ladies, Your Viewing Figures Just Went Up

Jack Harkness in Doctor Who

Considering all the things he saw, experienced, and did, Jack was always ready to throw in a quick comeback. So much so that when his clothes disintegrated in the episode Bad Wolf, Jack took it in stride. Even when he learned that he was now naked in front of millions of viewers. Jack's reaction speaks volumes about his flirtatious nature. However, what follows in the scene, is even more interesting.

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When Jack realizes he's in danger, he quickly comes up with a weapon to use against his enemies even though he isn't wearing any clothes at the moment. What this scene therefore demonstrates is that Jack is ready to fight for his life no matter the circumstances. That makes him a more capable fighter than his carefree demeanor might suggest. And it doesn't matter if Jack has to fight people, aliens, or androids, as he does in this scene.

3 I Was Just Saying Hello!

Jack meets Martha in Doctor Who

Of all the companions in the early seasons of the renewed Doctor Who series, Captain Jack Harkness was the most open person about his sexuality. It was the first time the series introduced a pansexual person, somebody who didn't care about gender. Jack was free in showing his affection to the people he liked, and he perfected the art of flirting.

So much so that the Doctor suspected even Jack saying hello to someone was his way of flirting. Jack's defensive reaction was just as funny as the Doctor's subsequent comeback: For you, that's flirting. However, no matter how much the Doctor might have complained, even he didn't protest when Jack kissed him and Rose goodbyes before he went to fight against the Daleks... something that led to his death, at least until Rose resurrected him.

2 Under The Sink!

Jack joins the TARDIS crew in Doctor Who

Just like some of Jack's other best quotes, this one makes more sense in the context of the scene in which it appears. When Jack wants to get rid of the bomb that's inside his plane, he discusses several options with his ship computer. The possibility Jack prefers is to get the bomb out of the plane by using an escape pod.

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The only problem is there's no escape pod on the ship. Jack asks whether the computer looked everywhere and when the computer says yes, Jack adds: "Under the sink?!" Fortunately for Jack, the Doctor and Rose show up before the ship explodes and whisk him to safety in the TARDIS. This also serves as the real beginning of their mutual adventures, as until now, the Doctor wasn't convinced whether Jack would make a good companion.

1 I'm The Man Who Can Never Die

Rose revives Jack in Doctor Who

When Rose brings Jack back to life, she unknowingly makes him immortal. That's something Jack learns the hard way multiple times while he waits to reunite with the Doctor all throughout the 20th century. When they finally meet again, Jack describes to the Doctor the various ways he died, including falling off a cliff, being trampled by horses, or being pierced by a javelin.

After everything that had happened to him, Jack finally came to the conclusion that he can never die. That had a negative impact on his life as he was forced to watch many people he cared about die while he continued to live. Unlike Jack's other iconic quotes which are more cheerful, this one points out the darker side of his life, one that was explored in greater detail in the spin-off TV show Torchwood.

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