Malorne is known as the White Stag. He, shockingly enough, takes the form of a White Stag. It is said that Malorne had worshipers long before Elune did, but we don't know if that means Malorne is an older deity or he simply found a place in the minds of mortals before the Moon Goddess. Malorne, like Elune, was not a fan or violence or war. Many wars, including multiple civil wars amongst the Night Elves, were stopped dead just by the appearance of White Stag. He's a freaking demigod, so that's not terribly surprising. When a demigod shows up, you pretty much stop what you're doing unless the thing you're fighting is scarier than that.
Supposedly, it is actually a Tauren myth that is one of the earliest written accounts of Malorne. This myth is called the White Stag and the Moon. The White Stag is known as Apa'ro to the Tauren, and the myth goes like this: A giant gang of Tauren gather together to hunt down great beasts, they hunt down Malorne, Malorne's antlers get caught in the sky because he's so huge. He can't get free, so he calls out for help. Elune shows up and offers to free him as long as he loves her in exchange.
And thus was Cenarius born. Gross.
While Malorne was romantically involved with Elune, he was involved with Ysera of the Dreaming in... other ways. Not like that, perverts. A partnership. A business arrangement, almost. They both had a very deep interest in nature and its well-being, and Ysera would later mentor Cenarius. Malorne held the ability to move fluidly between the mortal realm and the Emerald Dream at will, which is either a cause or a result of this relationship.
Malorne is most famous for his son, no doubt. A close second is his involvement in the War of the Ancients. The War of the Ancients was the Burning Legion's first visit to Azeroth, many thousands of years ago. To make a long story short, the demigods got involved to prevent the utter destruction of all life on Azeroth. Aviana, Ursol and Ursoc, and Agamaggan each took a role in the War in their own way, and one by one they were killed after leaving a tremendous impact. Malorne, too, went down during the War of the Ancients, and it definitely was not a minor note in the war.
After rushing into battle to protect his son from the grip of the Legion, Malorne raged across the battlefield, utterly massacring demons by the dozen. It was going well! Until Archimonde showed up on the scene. The two fought, one on one. In the end, it was Malorne that was defeated. The Defiler had snapped his neck, Solid Snake style.
Not even minutes after that, Archimonde left the scene and Malorne's reinforcements appeared. Alexstrasza, Soridormi, Ysera, and their flights showed up to help. As I'm sure you can imagine, Ysera was not happy about Malorne's death. A lot of demons died at her hands that day.
This isn't about the War of the Ancients though, so let me sum up the rest of the war for your: We won, and the world broke in half.
Malorne is believed to still be 'alive' but only in spirit, living on in the Emerald Dream. In the realm of mortals, well, he's pretty much gone. He's certainly left a legacy, though. Most of us should know what Cenarius did for the world (druids), and his descendants continued the tradition that Elune and Malorne started: Sleeping with weird things, and having weird children as a result. Cenarius himself would later be killed by Grom Hellscream and his Fel Orcs.
Remulos, Zaetar, Ordanus and an unnamed fourth are the direct descendants of Cenarius. The unnamed son was a massive jerk, so Cenarius disowned him. He went on to start a tribe of centaur. Zaetar wandered off on his own, got drunk, shacked up with Theradras and is the father of at least five centaur tribes. Ordanus was a pretty upstanding guy, and worked hard to repair the forests of Kalimdor after the most recent invasion by the Burning Legion. Unfortunately for him, the Horde lend the Shadow Council (you know, the guys that serve the Legion) a hand and kill Ordanus.
Remulos is the current highest ranking Keeper of the Grove and Son of Cenarius, despite being the youngest. He serves in Moonglade, which is likely for the best. As a place of peace, it is hopefully unlikely that the Horde will kill him there alongside the Burning Legion like they did to so many of his family members! ...er, right, moving on.
The Dryads are also descendants of Cenarius, though not all of them were born of him. All of the other Keepers also have children, but I'm certainly not here to paint you a family tree. Go questing in Kalimdor and see how many you can find.
To sum up: Malorne is pretty awesome, and pretty much any of the freaky looking humanoids on Kalimdor are either his fault, Elune's fault, or both of their faults.