@Grelrik  
With Khorne, in earlier editions, he was described manifest/look as even somewhat “orcy/orky”,due the greatest amount of violence, being created by orcs(or orks in 40k).  
Well, it is true Warcraft III Liches did take at least SOME artistic inspiration from Nagash, ie even looking Egyptian (due to Nerubian Egyptian and Mesopotamian elements) and aving chains, but I think still, in turn, Nagash current design and mini, was inspired by Kel’Thuzad.  
 
 

 
Note similar hats, coloration. But seeing Warcraft allready took inspiration from Nagash when designing their liches, so it’s fair game, I guess XD.
 
Arthas is indeed something of a mix of characters. Arthas’ armor, and “evil north” theme screams Chaos Warriors, and there are some vible similarities to Archaon in Arthas’ storyline, but it also seems inspired from Might & Magic VI(1998) and Heroes of Might & Magic III: Restoration of Erathia(1999). For example Kreegan are aliens who look like demons, and launch an invasion on Enroth. the Burning Legion, are demons, who behave like aliens, while launching an invasion on Azeroth. Both establish cults to help them(the Cult of Baa by Kreegan, the Cult of the Damned by the Burning Legion). Warcraft III though, essentially combined the Cult of Baa with Deyja(a country rulled by Necromancers), creating the Scourge/Cult of the Damned. As we know, the Scourge, corrupts Arthas from good guys, resulting in him finally taking over the Scourge, as the Lich King. Deyja corrupts Nicolas Gryphonheart, resulting in him becoming the Lich King, and taking over Deyja.
 
With Warcraft demons, World of Warcraft retconned with Warlords of Draenor that they are also unkillable, except if killed in the Twisting Nether XD.
 
Even currently, World of Warcraft does take inspiration from Warhammer. While many see the Nighborne introduced oin World of Warcraft: Legion, as based on Drow, they also have similarities to Druchii, especially as they were presented in Warhammer Online.  
 
 
 

 
Although Highborne Night Elves, allready had visible Drchii influence, with Azshara visibly taking from Morathi for example.

@BackgroundLoL  
Oh there was this thing I forgot, you mentioned nagash new models and miniatures being inspired on kelthuzad why left me with doubts and I started to search on my files trying to find the pic.  
 
This one is from 4th edition that was 91 or 92 if I’m not mistaken, it is true the designs at the beginning (80s) were not as awesome as they are now, but they started to be awesome on the 90s. A reason I think is valid is that they couldnt afford to show many huge sized characters cause they would be forced to make them big on the miniatures.

@BackgroundLoL  
Yeah I remember I had that as well, it was mentioned on borh first and second edition that orkz and orcs (40k & fantasy) worshipped chaos but the one they followed the must was khorne,specially since he was all about killing your enemy on the nost brutal way and also the “kunning prowess of battle”. On the very beginning of the story in warcraft there were not demons, there were daemons and I remeber in the manual a part speaking about a daemon who was collector of skulls. But there is also this thing of demons in warcraft being clearly killable. But then times goes by and they suddenly end up being inmortal and their essence flies on the warp, i mean nether… see? again.
 
Also arthas is just a mix of characters, all thrown in one story that is a little bit too convenient and makes the character just too overly powerful.

@Grelrik  
Well I somehow deleted by accident part of my resonse, were I stated Warcraft III was released in July 2002(months before the Necron Monolith was released), and the Necropolis was in previews and demos in 2001, but yeah if the Necron Monolith was allready in magazines in 1999-2000, yeah it may have inspired the Necropolis.
 
With orcs, I once argued that orcs(and orks) in neither Warhammer are connected to Daemons, as orcs were in the first two Warcraft games, but in very old Warhammer Fantasy editions(first and Second), orcs did indeed, worship Chaos Gods, at leat from what I researched(cannot find exact source now though).

@BackgroundLoL  
Now that’s better, don’t worry friend I was not trying to start something but I couldn’t answer completly until now (IRL interruptions).
 
To make it fair, yeah both companies pretty much copied some stuff or took inspiration from one another, there are conjetures about the origins of many things in warcraft, and I have read this thing of some names and portions of lore comming from other places. The truth is both opinions are correct, I was a warhammer fan after knowing warcraft but knew about warhammer long before warcraft. All due to a magazine, so yeah I decided to study and search for years.
 
The monolite I can argue that I saw designs of it on a magazine on 1999 or 2000, also warcraft 3 was released the same year 2002.
 
I would not like to make this a long discussion theme and start some “sheit” so yeah I think we can all agree wc took way too much from wh but it also has some other inspiration places. I noticed I sounded ablittle carried away but I’d like to make it clear that I have strong reasons, Really few people know the subject on an overall, specially where I live, so I think I grew used to sound harsh.

@Grelrik  
Well, It’s a bit more complicated. While Blizzard with Warcraft, takes a lot from Warhammer, they also take a lot of inspiration from other sources. Sargeras is partly based on Sargonnas from Dragonlance, for example, based Old Gods on Old Ones and Outer God’s from Lovecraft’s writtings(Although C’thun, might be named after the C’tan.)
 
Azeroth also has a lot of it’s own elements, like the Dragon Aspects, and the organic races, being largelly descended from mechanical construct. With flesh and free will, being part of the Old Gods “corruption”. Or the Dark Elves(Night Elves) being the original elven race, from which all others descended, and Night Elves being non-malocious.(It’s notable that in the oldest Wrhammmer sources, Dark Elves were also named Night Elves, and both live in the equivalent of North America…).
 
Both Warhammers, also took some vidual cues at the very least, from Warcraft. The Necron Monoliths(appearing first in September 2002), are based of the Scourge Necropolis from Warcraft III(Warcraft III, was released in July 2002, but the Scourge Necropolis structure shown in demos and previews much earlier).  

 
And Nagash’ current mini is based on Warcraft liches in design, particularly Kel’thuzad.
 
But yes, Warcraft did still take a lot of inspiration from Warhammer. The Warcraft 3 animated portraits, seem even to be inspired by the animated portraits in Warhammer video game Dark Omen 1998.

@Background Pony #04DA  
Well that’s what I used to think, I mean being angry with blizz for being so low and GW for going idiot mode, but then paul (forgot his last name) says that blizz was the one that backed downbon last moment because they wanted to do “their story” only to copy+paste story fragments and changing names for the next 20 years.

@Grelrik  
>people are still mad about Blizzard not scraping all progress they made then GW went idiot, as usual, and declined their offer

Oh look the warhammer copy, well, at least this dlc added something nice here to make it playable and forget the blatant rip off

at first look, i was thinking it was age of empires 2, but i was wrong

lol. that’s pretty amazing, if someone did that. :D

@firestorm  
Actually, it’s downloadable as a mod. You can see it as an “unoficial” DLC XD

if only that was a texture pack or some kind of dlc for wc2 :P

Damn dude, I wanna play warcraft 2 now!