The Vegas Golden Knights are in the Stanley Cup finals in their first year of existence. (Ethan Miller/Getty Images)

Perhaps the only thing more surprising than the Capitals’ ascension to the Stanley Cup finals is that of their opponent, the Vegas Golden Knights.

Led by former Washington general manager George McPhee, the Golden Knights were fifth in the NHL’s regular season standings, going 51-24-7. Goaltender Marc-Andre Fleury, who previously bedeviled the Capitals with the Pittsburgh Penguins, has powered the Golden Knights’ playoff run, posting a 1.68 goals against average. That’s about a third of a goal better than Washington’s Braden Holtby (2.04).

It took the Capitals 19 games to get through three rounds of the playoffs. The Golden Knights did it in 15. Their most recent game was Sunday, when they finished off Winnipeg in five games in the Western Conference finals.

So just who and what are these Vegas Golden Knights? Here’s a quick explainer:

When and how did Las Vegas get a hockey team?

The Golden Knights are an expansion team that played its first season this year after negotiations to launch a Las Vegas team began in 2014. Billionaire businessman Bill Foley fronted the money for the club and launched a season-ticket drive in 2015 that was so successful that his ownership group beat out a competing group representing Quebec City.

Were the Golden Knights supposed to be any good this season?

Well, most expansion teams — in every major American sport — aren’t very good in their first season. The Golden Knights are only the second team since 1990 in a major North American sports league to earn a spot in the postseason in its first season. The other team was the NBA’s New Orleans Hornets in the 2002-03 season, but the Hornets were an existing team that relocated from Charlotte. Every other debut team — all 18 of them — finished no better than next-to-last in their first season.

Deadspin, in a season preview, called the Golden Knights, “a bad, bad team,” made up of a couple of decaying stars and third- and fourth-line scrubs McPhee was able to scoop up in the expansion draft.

A few more preseason predictions:

ESPN: “A poker pro has a better chance of hitting a straight flush on the river than the Golden Knights have of making the playoffs.”

SB Nation: “Vegas will do their future selves a service by remaining at the bottom half of the league.”

The New York Times: “For now, the team may not have designs on the Stanley Cup or even the playoffs, but it does feature some prominent players.”

USA Today: “The Vegas Golden Knights could be better than we think, but they will make trades that will help their future and hurt their point total this season.”

The Hockey News: “The thin forward group and blue line leaves the Golden Knights without the requisite depth to fight their way out of the Pacific basement. If Vegas is shooting for a top selection in next year’s draft, though, they should be right on target.”

CBS Sports: “Outside of bringing to life the pure spectacle of pro hockey in Vegas, the Golden Knights can’t be counted on for a whole lot in 2017-18. There is simply too much talent in the Pacific Division, not to mention every other division that boasts players who have, you know, had more than a few months to gel, to think otherwise.”

Still, some hockey executives and analysts saw the beginning of something promising in the desert.

“They’re way past getting off the ground,” Nashville General Manager David Poile said after the expansion draft. “I think this is by far the best expansion team ever.”

What was this “expansion draft?”

When a new team enters the league, it needs players, so the NHL tells its teams they can “protect” a certain number of theirs, and the new team is free to poach those left “unprotected” to build its roster.

In the Vegas expansion draft, held in June, every NHL team had to either protect seven forwards, three defensemen and one goaltender, or any combination of eight skaters (forwards and defensemen) and one goaltender. That’s significantly fewer “protected” players than past expansion drafts allowed, leaving McPhee with some pretty good players to add.

The Golden Knights scooped up winger James Neal, who scored 23 goals last season with Nashville, and Fleury, a three-time Stanley Cup champion with Pittsburgh. Youngsters William Karlsson and Jonathan Marchessault have grown into first-line forwards. From Washington, McPhee took Nate Schmidt, one of the Capitals’ top defensive prospects.

How has this first season gone?

Really, really well. The Golden Knights are likely the best expansion team ever, in any sport. They won the Pacific Division by beating out Anaheim, San Jose and Los Angeles.

Karlsson, Marchessault and Reilly Smith were among the league’s top 10 in plus/minus in the regular season. After Vegas pulled off an eight-game winning streak that lasted half of December and boosted its record to 27-9-2, it was clear things were going right for Coach Gerard Gallant and company.

What players should I know to impress my friends?

Definitely Marchessault, Karlsson and Smith. That’s the Knights’ top line, and Washington could struggle with its speed and scoring ability. Together, those three have lit the lamp 108 times this season.

Also, keep in mind Neal, the Nashville import who played in the Stanley Cup finals this time a year ago. Cody Eakin and David Perron are two more names to know. They power the Vegas third line.

Is the team “Las Vegas” or just “Vegas?”

It’s just Vegas. Don’t ask.

And what’s this I hear about the pregame show?

T-Mobile Arena has gone all out with elaborate pregame displays featuring a knight mascot against some representation of the opponent, often in medieval dress. Naturally, the knight wins and prepares the fans for battle, or at least a hockey game.

Here’s an example of what Vegas pulled out for the Western Conference finals.

Finally, who’s favored to win the Cup?

Vegas, surprisingly. The Golden Knights opened as minus-135 favorites (meaning you must wager $135 to win $100), while the Capitals were plus-115 underdogs (wager $100 to win $115), according to OddsShark.

More on the Capitals:

Jinx this: Alex Ovechkin touched the Prince of Wales Trophy — and carried it home

Capitals fans unleash the joy: ‘I want to high five everyone in here right now’

Game 7 swung on the unlikely stick of Andre Burakovsky

On social media, an outpouring of emotions (and champagne)

Here’s what was happening the last time the Capitals advanced to the Stanley Cup finals