Mace of Spades is translated to "Morgenstern" in the German and french versions of the game. "Morgenstern" is in German the name of the weapon he uses. Morgenstern is also a song by Rammstein. Translated back to English, Morgenstern means "morning star", a category of spiked, medieval mace-like weapons.
Before his story was changed, it stated that he originated from the Shadow Isles. Now it states that "a being like no other emerged from the forgotten alleyways of Noxus." However, associate writer RiotRunaan posted on the League of Legends forums "Do bear in mind that it only states that the Master of Metal emerged in the alleyways of Noxus, nothing more." This indicates that the original story might still be canon.
Kitae confirmed that Mordekaiser is definitely from the Shadow Isles.
Mordekaiser is known for stalking the slums in Noxus.
Mordekaiser is in the metal band Pentakill with Sona, Karthus, Olaf and Yorick. According to the Journal, the band is said to be successful across Valoran.
Mordekaiser and Hecarim know each other, and are stated to have similar beliefs, but disagree when it comes to how they achieve their goals.