The runes of warding

The runes of warding are a set of runes found inside Molten Core. There is seven of them in total, each having its own name, and seem to somehow protect Ragnaros who is sleeping in his lair. They are they key to summoning Ragnaros as a boss.

Notice that the name "the runes of warding" is mentioned only once (by Majordomo Executus).

Details
Each rune only appears on one location, and the runes never swap places. Each rune is also guarded by one of Ragnaros' lieutenants, namely Magmadar, Gehennas, Garr, Baron Geddon, Shazzrah, Sulfuron Harbinger, and Golemagg the Incinerator. The runes are initially active and deactivates one by one when their respective guardians are killed. When all the runes are deactivated, Majordomo Executus will spawn. When he is defeated, he will surrender to the player(s) and offer to summon Ragnaros.

Changes
Prior to Patch 3.0.8, each rune had to be deactivated by "dousing" it with either Eternal Quintessence or Aqual Quintessence. These liquids were sold by Duke Hydraxis.

Other appearances
The runes of warding can also be found on the walls in Ragnaros' Lair. Game-mechanics-wise, unlike the guarded versions, they do not seem to hold any purpose other than being decorative. Their presence do however indicate, lore-wise, that the runes of warding are connected to Ragnaros. They also appear in the TCG (Molten Core Raid Deck), as well in the Molten Core April Fools joke as letters.

The runes

 * The Rune of Kress is guarded by Magmadar. Both it and he are found in Magmadar Cavern. The rune is located in front of him on the floor.
 * The Rune of Mohn is guarded by Gehennas. The rune is located in front of him on the floor.
 * The Rune of Blaz is guarded by Garr. It can be found on the floor near him and his adds. As they wander around a little, they sometimes step upon it.
 * The Rune of Zeth is guarded by Baron Geddon. It can be found on the ridge (or "bridge") behind Golemagg the Incinerator. Baron Geddon patrols the cavern continually, and will only be near the rune when he occasionally approaches it on his patrols.
 * The Rune of Mazj is guarded by Shazzrah. It is located on the floor in his cavern. He is constantly strolling around it.
 * The Rune of Koro is guarded by Sulfuron Harbinger. It can be found in front of him on the floor.
 * The Rune of Theri is guarded by Golemagg the Incinerator. It can be found in front of the core hound on his right side, on the floor.

Speculation
Lucifron is unique as he is the only boss in the Molten Core which seemingly has no connection (other than being an ally of Ragnaros) to the runes of warding. Although initially present in the instance, he doesn't guard any runes, and it's possible to summon Majordomo Executus without killing him. A possible explanation may be that he is actually watching over both Magmadar and the Rune of Kress, as Magmadar is an animal and therefore doesn't possess any real zeal to protect the rune. This theory matches how Lucifron and Magmadar is found on the same location and the Tome of Tranquilizing Shot (given that Lucifron was given the book as a means to keep Magmadar in check). Oddly enough, it is however still possible to kill Magmadar without killing - or even alerting - Lucifron.