Who is Lorkhan and why is he so important? What's this about the Heart of Lorkhan and the moons? I don't remember any of this from the games...Well TES4 as I can remember.

http://imperial-library.info/content/morrowind-monomyth

Quick Note: Men like him (save for Redguards), and elves hate him (save for Dunmer). Men like him because they believe he performed a divine mercy to allow lowly mortals become greater than the gods, and elves hate him because they feel his creation of Mundus removed everyone's god-like awesomeness god powers and turned them into lowly mortals.

Lorkhan is a crazy guy who tricked the Aedra into making Mundus, then had his heart shot into a sea, and "died." His corpse split into two moons, Masser and Secunda (or Jode and Jone, depending on who you ask). His spirit kind of influences everybody on Nirn, cause that is just the kind of person he is.

Only the elves believe it was a "trick," the arrogant mounds of ghral feces.

I agree, it was a wonderful thing Lorkhy did! Hm... Hey! Wouldnt I be smart to worship Lorkhan? He [censored] made Mundus and thereby us (people in Tamriel) in a sort of sense! The Aedra though... Seriously... Wasnt the cost worth it?

Well, if you look to the Cyrodiilic creation myth, the men aedra thought that despite the sacrifices it was worth it and the merish aedra hate it. I find the Cyrodiilic myth to be the most fun as it separates Akatosh and Auri-el (or something like that)

In case you don't have time to read the links (which you should), in a nutshell it was his idea to create Mundus. He http://tvtropes.org/pmwiki/pmwiki.php/Main/TricksterArchetype other spirits into sacrificing themselves for this creation. Some of them rebelled and became Daedra...the Aedra ended up dying or becoming severely weakened. Some of them http://tvtropes.org/pmwiki/pmwiki.php/Main/KilledOffForReal and are now dead - the Earth Bones. Others became http://tvtropes.org/pmwiki/pmwiki.php/Main/OnlyMostlyDead and became Divines.

Really, men liking Lorkhan is not particularly accurate. The Redguards don't really and he is an antagonist to the Bretons. Thats a solid half the (genetically) manish populations don't share the stereotypical "yay, Lorkhan" worldview

Bretons are menmer, so they don't count! And my use of...ah screw it, I don't feel like arguing semantics here. I'll save that for a rainy day.