Zed is the 1st champion whose death animation shows him escaping (via a shadow portal), rather than actually dying. Whether he actually manages to cheat death remains open to debate. A video can be seen here.
Also his Shockblade skin has a different animation. Instead of crawling into a shadow portal, a bolt of lightning strikes him and he disappears. A video can be seen here.
Zed is the 5th champion to utilize energy as a resource.
Zed's dance is inspired by various martial arts. The animator that formed the idea is a black belt.
Zed's name is similar to the name of the antagonist organization from the classic Genesis Shinobi series, where the organization is known as "Zeed" and later "Neo Zeed". Furthermore, in the game "Revenge of Shinobi", Neo Zeed kills the protagonist's master.
Shockblade Zed's blades are likley a refrence to the hidden blades from Assassin's Creed
This is especially shown in a critical stike when the blades retract into his sleeves after the attack
Zed and Shen were taught under the same master, Shen's father, and were rivals to one another.
Zed would later murder Shen's father and establish a new ninja order, the Order of the Shadow.
In "G.I. Joe: The rise of cobra" There were two ninjas (Snake Eyes and Storm Shadow) who were under "Hard Master's" supervision and were learning martial arts, both were adopted. Then suddenly, one of them, Storm Shadow, felt like Master was giving to much attention to his other student and killed his master when he was not ready to defend, and then ran away unchased. This might be a reference to two skins that Zed has and might also be that someone is trynig to compare Shen to Snake Eyes and Zed to Storm Shadow who just like Zed killed his father (master).
Zed seeks to abolish the old ways of balance and replace them with the forbidden art of the shadow. Any ninja who refuses to learn will be eliminated.
According to Runaan, Akali may have some former connection to Zed. What that connection was has yet to be elaborated on.