Don't mind him, laddie. Thorin has more cause than most to hate Orcs. After the dragon...

Balin:

Don't mind him, laddie. Thorin has more cause than most to hate Orcs. After the dragon took the Lonely Mountain, King Thror tried to reclaim the ancient dwarf kingdom of Moria... but our enemy had got there first. Moria had been taken by legions of Orcs, led by the most vile of all their race, Azog the Defiler. The giant Gundabad Orc had sworn to wipe out the line of Durin. He began by beheading the King. Thrain, Thorin's father, was driven mad by grief. He went missing, taken prisoner or killed; we did not know. We were leaderless, defeat and death were upon us. That is when I saw him; the young dwarf prince facing down the Pale Orc. He stood alone against this terrible foe, his armour rent, wielding nothing but an oaken branch as a shield... Azog the Defiler learned that day that the line of Durin would not be so easily broken. Our forces rallied and drove the Orcs back; our enemy had been defeated... but there was no feast or songs that night, for our dead were beyond the count of grief. We few had survived and I thought to myself then 'There is one I could follow. There is one I could call King'