Orcs of the Misty Mountains
This article or section needs more/new/more-detailed sources to conform to a higher standard and to provide proof for claims made.
Their origin, and when they settled those tunnels is not known. Sauron must have taken at least some control over them when he settled in Mordor. By the end of the Second Age they must have done the First Sacking of Gundabad and drove out the Dwarves. Orcs of Mordor had come among them, and under their command they ambushed and killed Isildur at the Battle of the Gladden Fields in early Third Age.
After the fall of Moria in Third Age 1981, Orcs of the Misty Mountains entered and occupied its ruins. In Third Age 2509, on a trip to Lórien to visit her parents, Celebrian was waylaid by Orcs in the Redhorn Pass. She was captured and tormented, receiving a poisoned wound until her sons rescued her.
Long afterwards, Moria became the seat of an Orc-chieftain named Azog who slew King Thrór of the Longbeards, and so started the War of the Dwarves and Orcs. In Third Age 2793 the Dwarves attacked, assailing and/or sacking one by one all the Orc-holds they could from sacking Mount Gundabad in the north, to the Gladden Fields in the south. Most of the war was fought underground, in the great mines. During the conflict many thousands of Orcs fleeing south through Rohan, trying to claim a refuge in the White Mountains beyond, troubled the Rohirrim for two generations. The war ended with the Battle of Azanulbizar where Azog himself was slain.
The Orcs of the Misty Mountains virtually disappeared as a threat for Eriador and Wilderland but the Dwarves were unable to reclaim Moria. Around Third Age 2747 the Orcs became more bold, daring to invade Eriador. The Rangers of the North fought many battles trying to hold them back, but one party managed to reach the Shire. They were fought off by a party of brave Hobbits under Bandobras Took, who killed their leader Golfimbul in the Battle of Greenfields.
After that, the Orcs lurked among the Misty Mountains, and in Third Age 2941, a group of them under the leadership of the Great Goblin, captured Thorin and Company in the High Pass. They escaped with Gandalf's help, killing the Great Goblin in the process. Soon after, Azog's son, Bolg united the Orcs of the Misty Mountains and led them east to fight the Battle of Five Armies. That battle ended in defeat for the Orcs, and left the Misty Mountains free of them for many years afterwards.
By the time of the War of the Ring, the Orcs of the Mountains reclaimed Moria but fell under the command of Sauron and Saruman. There were Orcs from the Misty Mountains, in the party that captured Merry and Pippin at Parth Galen.
Legend says that the Longbeards eventually succeeded in recapturing Moria, so the power of the Orcs in the Misty Mountains must have waned considerably after the Third Age if they survived at all.