The Two Handed Great Ruler is, in all aspects, a clone of the Great Sword, aside from having a lower unlock level. Despite its slow charge, the Great Ruler is capable of tremendous damage if readied fully, and is reasonably compact, though not to the great extent of some knives, which somewhat limits its utility in Stealth/Dodge builds.
The Two Handed Great Ruler is based upon a 100cm metal ruler that has its measuring edge sharpened into a blade. It seems to have been reinforced somehow, as its tensile strength is utterly ridiculous for a ruler, seeing how items of such type are usually bendy and/or flexible enough to be able to be distorted enough for storage, or to reduce stress on the ruler body as a whole to prevent breakage.
This weapon is a nod to the h3h3productions reaction video "Two Handed Great Sword", where Ethan pretends to use a ruler as a sword, which predictably is vastly more floppy than the game version, being a ruler and all.