I read much information about those two guys,a demigod of fire and forge Ornn,and a demigod of thunder Volibear.
In true,when Ornn was revealed,i was curious about why Volibear wanted to fight with him own brother,but after reading the new short story,**Silence of the damned**,i get it,it's only a theory but it have sense.
By my opinion,Volibear was corrupted by something ancient and evil.Why i think he was corrupted?well,let's see one Ornn quote:
This quote will say Ornn when he moves near Volibear:
**"Singed fur... Jealous blood... My brother is near!"**
At the first sight i didn't attach great importance to it,until i read the short story,there we can find a thing,what shows to us what with Volibear something happens,because not just like that Ornn say "**Jealous blood**",as i think the word "Jealous blood" it's metaphor.
Here one moment from the short story:
"** From its mouth, an unnatural, black blood dripped.**",black blood..there is something wrong,it is?
Here is my theory about this:
When Ornn was forging and teach the humans to blacksmithing,Volibear find on the outskirts of Freljord something mysterious,from curiosity Volibear come near to **it**,and that thing corrupt him mind and make him to fight against him own brother Ornn.
As i hear,Volibear is on the rework list of Riot's,and i hope my theory will be as half right,
because it fits well as i think.