Zod

If you look at the list of all runes, you can find out the cube recipes to create a rune of one level higher than Zod. Here are the Zod attributes:

Rank: (r33)
Weapon: Indestructible
Armor/Helm/Shield: Indestructible
Ilvl/Clvl Required: 69

Zod is the highest rank of rune available, and does basically never drop. You will mostly have to take runes of lower rank and use the Cube to upgrade them to a Zod rune. The full transmutative list can be found here.