"...and so, locked beyond the gateway of blood, and past the hall of fires, Valor awaits for the hero of light to awaken..."— Quest summary(src)
Arkaine's Valor is a piece of armor found in Diablo I, and can only be found in Single Player as the reward for completing the Arkaine's Valor quest. It is extremely useful at that point, because it is virtually guaranteed to be a considerable upgrade over any armor found to that point in the game. The usefulness of this armor declines as one's character moves deeper into the labyrinth since the Armor Class is not very high, but it is not uncommon for low Strength characters to wear it all the way through Normal difficulty and beyond, thanks to its Fastest Hit Recovery affix; a great tool for preventing stunlocks.
The armor can be sold for 10,500 gold.