I've heard he upgrades the Horn of Valhalla. The only problem is, I can't find him everywhere. Where can I find him?

he is in the Wawakeen(sp?)promanade

I heard that, too. But...I have searched every square inch of the Promenade (or so I thought) without finding him. Can anyone give a more specific location?

Just north of the left exit from the Promenade (before the tunnel) there is a raised platform of sorts. Maheer is there, along with a guy called Quataris (who deals in art).
Alternatively, do you know where the ore merchant is? (Look at the game map if you don't - it's marked). Maheer is to the right (east) of the ore merchant on the platform.

Thanks,

I'll look there again, although I'm sure I've walked right through there numerous times without seeing him--both day and night. I suppose it might be a bug in my game.

The little textbox that pops when you hover the mouse over persons/items doesn't tell his name. You have to talk to him to know who it is, you also have to ask him if he does anything special, and he will tell you about the horn crafting