How to set my antagonist apart? Too much like Voldemort? *POINTS AND FAVORITE TO BEST ANSWER!?

So, my antagonist is a sorcerer named Mercer. He is the ancestor of the protagonist, Stetson.

Mercer was part of "The Great Four," a group of wizards and witches (2 boys, 2 girls, all siblings) who upon their father's death acquired a fragment of his weapon. His weapon is called the Reaper, and it was a 3 bladed scythe.

The reaper allowed you to "reap" a victim, and gain his "focus." Now, "focus" is like attention span or imagination. To perform magic, you must use your focus to clearly envision the magic you want to happen and channel it. Since it essentially uses brain power, it is a deplete-able source.

Anyways, he thinks that since they have the fragments (which even alone are very powerful) they should be treated like royalty. He thinks they are above the rules and that everyone should do what they say.

The other siblings don't agree. They believe they are simply peacekeepers among the people. Ones who were granted power in order to help benefit the world. Mercer eventually creates a new form of magic called will bending, which allows a person to completely control another. When his siblings find out, they are furious and banish him from the *town they live in.

Anyways, he finally comes back with a sort of army of followers, and attempts to steal the other pieces of the Reaper from his brother and sisters. Along the way, he kills anybody who stands in his way, even the most innocent.

He is completely mad and is bent on reassembling the Reaper. Anyways, he finally comes back and engages in a war with his siblings. They aren't able to defeat him, but they are able to send him to the Other Realm.

The Other Realm is a place where one does not live or die, they merely exist. The laws of magic and time are completely skewed, meaning his magic is almost useless and time is about 20X's slower than normal.

Knowing that he will not be held for long, they each sacrifice themselves to seal him away and save the world. In doing so, they each create a portal to the Other Realm. The portals are hidden away so that no one will ever find them. Also, each piece of the Reaper is hidden as well.

Anyways, in present day, Stetson ends up getting dropped off in this town by his family. It is named Incantor, and it is actually thousands of years old. Imagine a town that Tim Burton would imagine- Skewed windows, creepily amazing architecture, everything. Anyways, he finds out that he is actually a relative of the Great Four, actually the other brother who defeated Mercer.

He finds out that he has magical powers. Mercer and his followers have found the portal out of the Other Realm, and they are using it to slowly escape back into the real world. Eventually Mercer will return to reassemble the Reaper and take over.

Him and his two cousins (also descendants) must find and unravel the clues to help them each find their pieces of the Reaper as well as the portal that the evil is escaping from.

Okay, here is the thing. Mercer's only goal is to come back and reassemble the Reaper so that he will be all powerful. He plans on killing anyone who gets in his way and transforming the world into a place where those who have magical powers basically enslave those who don't. He, of course, will be on top.

So, my main concern is- Do his motives sound too similar to Voldemort's? Like, I'm trying to create a character that is creepy and ruthless, but I feel he is too similar to Voldemort.

Could he have other motives? How can I make him more different? PLEASE HELP ME!

I REALLY don't want people to feel I'm trying to rip off Voldemort or Harry Potter. So again...PLEASE HELP ME!

POINTS AND FAVORITE TO BEST ANSWER!