If you dig deep enough, you can find roots of the Commander and EDH format going back to some of the earliest history of Magic. To make a long story short, the ball started rolling in the early 2000s, but it's only in the last few years that it's really picked up steam - all but becoming the de facto casual format for constructed Magic. Certainly getting officially supported by WotC with products has helped with that, but the format's success pulls on a number of subtle strings.
It's designed to be social and multiplayer with an emphasis on being laid back, though you can play it more seriously. Deck construction naturally lends itself to simple to grasp through lines. Hell, it's even easier to swallow and justify the cost of an expensive card when you only need one of them.
For the last several years WotC has been putting out Commander products and there's even been a shift in card design in the regular releases. For instance, the phrase "each opponent" is way more common lately. Let's be honest, there have been a few stumbles along the way with MSRP and availability, but WotC seems committed to stepping up their Commander line to a yearly release. Commander 2011 and 2013 explored three-color wedges and shards, 2014 was mono-colored with planeswalker generals, and 2015 is set to explore the enemy color pairings. Commonly referred to as Orzhov(White/Black), Izzet, (Blue/Red), Golgari (Black/Green), Boros (Red/White), and Simic (Green/Blue).
I'm going to run down the spoiled ten generals and give some initial ideas of what you might build around them, though the last few Commander products have been very playable right out of the box. This won't be the only way to utilize them however. Keep in mind that this will be through the lens of my own Commander group, which is squarely anti-combo and degenerative strategies like mana denial.
Daxos the Returned
Due to the popularly and necessity of board sweepers in Commander, tokens are naturally a pretty popular strategy. While folks are still reeling from getting their board wiped out, you can rebuild much faster since most of your cards are built in as several creatures. This typically gets supplemented by various Glorious Anthem effects, which are multiplicatively effective when you're making lots of creatures. Daxos the Returned comes down early picking up experience from your Cathars' Crusade, Intangible Virtue, and such, and then in the late game you can use him as a Mobilization that spits out much bigger creatures.
Karlov of the Ghost Council
Obviously Karlov of the Ghost Council is going to end up in some kind of lifegain matters deck, perhaps letting Oloro, Ageless Ascetic sit in the big chair instead. Ideally Karlov of the Ghost Council wants to be around a lot of small lifegain ticks rather than big bursts. The extort mechanic, like Crypt Ghast and Pontiff of Blight, the Soul Sister style cards, and Sun Droplet are perfect pairings. Generals like Karlov of the Ghost Council are usually used to disrupt their opponent's plans and play politics until they can build up or land a win condition. Though it's not impossible to deal 21 damage with Karlov of the Ghost Council either, just because you can use the counters to kill things doesn't mean you can ignore that he's an Ajani's Pridemate that grows twice as fast. Expect some hear some jokes about Karlov going to ghost gym and getting buff.