Plenty of adjectives come to mind when describing literature's greatest detective, Sherlock Holmes: Brilliant. Unflappable. Relentless.

But sexy? Now that's one we haven't heard too often.

That is, not until Benedict Cumberbatch put a modern-day spin on the iconic role in the BBC's reboot of the classic Sir Arthur Conan Doyle mystery series. Since "Sherlock" debuted in 2010, Cumberbatch has rapidly shot to worldwide fame — and amassed a remarkably devoted fan following.

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We witnessed this devotion firsthand during PBS's winter press tour earlier this month, when Cumberbatch arrived to promote the third season of "Sherlock" (which wraps up this Sunday on PBS). Normally, these press tours are trailed by a few scattered paparazzi and autograph hounds, even though A-list stars are a regular sight. But on that day, more than a dozen Cumberbatch fans camped out all afternoon, holding signs and waiting patiently for their idol to arrive.

The jaded TV critics assembled there all agreed: We hadn't seen anything like this in years. And social-media sites like Tumblr are filled with adoring shrines to Cumberbatch and his "Sherlock" adventures. So what is it, exactly, about this man that inspires such a frenzy? We reached out to some of his biggest fans to shed some light on the phenomenon, and give us a peek inside the "CumberCollective." (Their preferred term, but we'll get to that.)

"Cumberbatched" at first sight

"Sherlock" producers Steven Moffat and Sue Vertue first took notice of Cumberbatch when he played a sinister family friend in 2007's "Atonement." In fact, he was the only actor they auditioned to play Holmes — but even they didn't think they had a burgeoning sex symbol on their hands. As Vertue told Entertainment Weekly, "When we first cast him, people were saying, 'You promised us a sexy one!' People weren't thinking of him in that light at all."

[Photos: Get to Know Benedict Cumberbatch, A to Z]

But Cumberbatch soon won over doubters with his fresh take on the legendary sleuth. Rather than the tweed-clad professor-type with pipe and magnifying glass in hand we're used to seeing, Cumberbatch's Sherlock is firmly rooted in the 21st century, combining his massive intellect with tech gadgets like smartphones and GPS to solve cases. Add in his comically antisocial demeanor (Sherlock often refers to himself as a "high-functioning sociopath"), and he comes across as a bad-boy genius — the perfect mix of rock star and rocket scientist.

Naomi Roper, who owns and edits the popular fan site Cumberbatchweb, remembers the first time she saw Cumberbatch as Sherlock: "I sat down to watch it, and five minutes later, I was hooked." Soon after, she went to see the actor in the 2010 revival of the Terence Rattigan play "After the Dance," and "he just blew me away. I set up the website the next day."

Kristina Manente has always been a Sherlock Holmes fan; her Baker Street Babes blog and podcast cover all iterations of Holmes. But she had no interest in watching the Cumberbatch version at first because, as she says, "I thought a modern Sherlock Holmes was stupid." She eventually caved in, though, and when she saw Cumberbatch's award-winning performance as physicist Stephen Hawking in 2004's "Hawking," she "was immediately floored by his talent."

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According to Lauren Gallaway, who co-hosts the Fancastic blog and podcast, there's even a word for the moment a fan falls under the Cumberbatch spell: "It wasn't until someone gave me a 'Sherlock' Season 1 DVD that I was, as we say, 'Cumberbatched.'"

"Well, he's rather good-looking, isn't he?"

And the success of "Sherlock" has paid off in spades for Cumberbatch. Steven Spielberg offered him a role in "War Horse," telling Empire magazine that Cumberbatch was the best onscreen Sherlock he'd ever seen. And last year, the actor was seemingly everywhere, from playing superhuman villain Khan in "Star Trek Into Darkness" to voicing Smaug the dragon in the latest "Hobbit" film to co-starring in Oscar-nominated films "12 Years a Slave" and "August: Osage County."

Watch Cumberbatch talk about his "Star Trek" role in this "Late Show" clip:

Still, Cumberbatch is an unlikely matinee idol. After all, he's not a strapping hunk in the conventional sense; he's pasty, thinly built, and a bit odd-looking. (Before "Sherlock" debuted, U.K. newspaper the Guardian made note of his "interesting" features, which sounds like something you say to be kind.)

Sure, the accent helps, but that doesn't explain his British fans; the Season 3 premiere of "Sherlock" drew 9.3 million U.K. viewers, more than double the U.S. viewership. And no offense to Jonny Lee Miller, but he's also British and is also playing a present-day Sherlock (on CBS's "Elementary"), and he doesn't seem to inspire nearly the dedicated following that Cumberbatch does these days.

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If you're trying to solve the mystery of Cumberbatch's appeal, though, there's a simple solution: Just ask his fans. "He's a fantastically talented actor, a total chameleon," Naomi says. "Plus, he's intelligent, charming, and very polite and gracious with his fans. He's surprisingly humble, given his recent meteoric rise… and well, he's rather good-looking, isn't he?"

Maria Fleischhack, also of Baker Street Babes, admires his commitment and range as a performer: "He dives into his roles, and every character he plays is distinctly different from the others he has played before. Just compare his performance in 'Hawking' with that in 'Sherlock,' and you have two entirely different super-geniuses next to each other who have nothing in common."

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And like most fans, they've all gone to extraordinary lengths for their love of Benedict. Naomi and Kristina both report waiting in line for hours to see him live on stage. (Kristina: "I camped out overnight for ten hours to get a ticket. It was in March, and it was absolutely freezing. Worth it, though.") And Lauren admits, "I may have dressed up like a femme Sherlock at San Diego Comic-Con in 2012. Blue scarf and all."

Several of them even made the ultimate sacrifice: going to see Cumberbatch play Wikileaks founder Julian Assange in "The Fifth Estate," one of 2013's biggest box-office flops. Naomi saw it (and liked it!), but allows, "I can't hand-on-heart say I would have rushed to see the film if Benedict wasn't starring in it."

They're not Cumberbitches, they're Cumberpeople

Sensing a trend, the media leapt on the growing Cumberbatch following and dubbed his female fans "Cumberbitches." A catchy name, to be sure, but one that's been roundly rejected by every fan we spoke to.

"I really do not like that word," Lauren says, with Maria calling it "definitely not a term I identify with." Naomi refers to "Cumberbitches" as "a term the media use for the fans, not a term the fans use for themselves. My usual comment is, 'I'm no one's bitch.'"

Although to be fair, a certain segment of the fandom still embraces the term — like the @Cumberbitches Twitter handle, which boasts 112,000 followers:

By no means do we expect fans to call themselves cumberbitches'. You can use whatever moniker you desire, but we're quite happy with this. — Benedict Cumberbatch (@Cumberbitches) January 22, 2014

So whether youre a cumberbitch, a cumberlady, a cumberbabe, a cucumber, a cumbercookie or a ben-addict or anything else, that's great! — Benedict Cumberbatch (@Cumberbitches) January 22, 2014

The generally accepted alternatives, in case you're wondering, are "Cumberbabes" or the more inclusive "CumberCollective" — a term Cumberbatch endorsed on "The Graham Norton Show." Yes, even the man himself has weighed in on the Great Cumberbitch Controversy, and he sides with the non-bitch faction. "I won't allow you to be my bitches," he told the Radio Times last year. "I think it sets feminism back so many notches. You are… Cumberpeople."

Watch Cumberbatch on "The Graham Norton Show" right here:

Not to mention the fact that Cumberbatch has plenty of male fans as well. (Yes, guys like "Sherlock," too!) Although "women and girls tend to be very forward and outspoken with expressing appreciation for him and his work," Kristen says, "I can safely say that I know as many male as female Cumberbatch fans." So just to be safe and P.C. about it, let's all just strike the term "Cumberbitches" from our collective vocabulary, shall we?

"I've actually never heard of a bad fan encounter with Benedict"

But whatever they call themselves, one thread connects all of Cumberbatch's fans: They all marvel at how gracious and generous he is with them. A following as fervent as his might understandably turn any actor into a closed-off hermit. But by all accounts, Cumberbatch goes out of his way to spend time with and accommodate the CumberCollective.

Each of the fans we spoke to have met Cumberbatch in person, and each speaks glowingly of the experience. "I've actually never heard of a bad fan encounter with Benedict," Lauren says. Maria remembers meeting him after a London theater performance, and "while he was exhausted, he stayed with the fans for a long time and took great care to sign things and to have his picture taken."

"He always takes the time to really talk to people, if he can, and gives them his full attention," Kristina reports. "He's very sweet and charming." And indeed, we saw this during PBS's winter press tour: After a long day of interviews, Cumberbatch insisted on meeting with the fans waiting outside, signing autographs, snapping photos, and taking time to speak personally with each one of them.

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And the benefits of the fandom extend beyond the man himself. Members of the CumberCollective have made real friendships after bonding over their mutual love of the actor. As Lauren says, "Our initial interest is our admiration of Benedict, but as we interact everyday over social media, we become friends."

They've even used their shared passion to do a little good. "There have been so many fundraisers and charity rallies in his name, which have raised tens of thousands of dollars," Kristina says. "It's quite lovely." Naomi's site holds an annual charity fundraiser on July 19, Cumberbatch's birthday. "Over the past two years, we've raised £25,000 for Myeloma UK and The Teenage Cancer Trust," she reports.

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Cumberbatch thanked his fans for their dedication during that day's "Sherlock" panel as well: "It’s kind of extraordinary and a little bit unnerving. I’ve got to acknowledge with gratitude the fact that they are so supportive, loyal, by and large intelligent, and some of them normal. [Laughs.] And committed to something that I really love doing and a character that I like playing. So yeah, it means a lot to me. It means a hell of a lot to me."

And his kindness and humility mean a hell of a lot to his fans, too. "They always say, 'Don't meet your heroes,'" Lauren says. "This is definitely not true for Benedict. He is one hero who I hope everyone can be lucky enough to meet."

The Season 3 finale of "Sherlock" airs Sunday, Feb. 2 at 10 p.m. on PBS.