A word/phrase for someone who changes the world

Sine Qua Non might work. It means, loosely speaking, a necessary condition, so it might convey the idea that the person was key to the new order of the world. It is a bit of legalese, but lofty, and therefore suitable as an epithet.

You were not looking for Aftermath, I suppose (because of the negative connotation). However, other compounds beginning with After- might work.

I don't know if either of these work perfectly, but I think they're worth considering. Both describe a very influential person in a neutral(ish) way.

Doyen carries the connotation of a leader or prominent figure who has already risen to the top. Doyen is often positive (the doyen of international finance), but you could just as easily be the doyen of organized crime.

a : the senior member of a body or group

b : a person considered to be knowledgeable or uniquely skilled as a result of long experience in some field of endeavor

Another to consider, someone who is known for challenging a tearing down fundamental institutions is iconoclast

1 : a person who destroys religious images or opposes their veneration

2 : a person who attacks settled beliefs or institutions

You can consider the phrases great mind or creative genius. These terms are often associated with people who changed the world. I think the terms can serve as a grandiose title as well.

Here is the intro paragraph of an article titled "Creative Genius: The World's Greatest Minds" from livescience.com:

News of the death of Apple founder Steve Jobs on Oct. 5, 2011, has been received with sadness, admiration and gratefulness for a man considered a "creative genius" who "changed the world" in many ways. In addition to Jobs, plenty of great minds have challenged paradigms, opened windows into worlds we didn't even know existed, and produced innovations that have persisted through time. Here's a look at the world's titanic thinkers, from Charles Darwin and Albert Einstein to Stephen Hawking.

Note: Another bonus term is a titanic thinker from the same excerpt. Also related is an innovator but it might not convey the idea by itself, so you can consider the phrase world-changing innovator.

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Additionally, there is simply world-changer as a self-explanatory term. The term is even listed in OED and there is an example from 2000:

So what makes The Beatles world-changers as well as best-sellers?

_{Andrew Calcutt · Brit cult: an a-z of British pop culture}

I don't know how common you'd like this word to be, so I'll offer you some unusual choices. The 'Tirthankara', less gloriously called a 'Jina':

In the Jain religion, one of the twenty-four founding prophets or Jinas, venerated as having successfully crossed the stream of time and having made a path for others to follow.

["Tirthankara, n.". OED Online. December 2015. Oxford University Press. http://www.oed.com/view/Entry/202498 (accessed February 03, 2016). Or 'Jina', see also Dictionary of Unfamiliar Words by Diagram Group. S.v. "tirthankara." Retrieved February 3 2016 from http://www.thefreedictionary.com/Tirthankara .]

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A more stolid and thus more neutral term--nothing grandiose about it--is the simple 'Change-Agent'.

change agent n. one who initiates a movement toward social change in a group.

["change, n.". OED Online. December 2015. Oxford University Press. http://www.oed.com/view/Entry/30467?redirectedFrom=change+agent (accessed February 03, 2016).]

This term has unfortunately been co-opted by business of late:

Change Agent
An employee or outside consultant who believes that he/she is making positive changes to a company. The term is used most commonly when certain employees encourage the use of new technologies. These changes may or may not be popular among other employees.

[Farlex Financial Dictionary. S.v. "Change agent." Retrieved February 3 2016 from http://financial-dictionary.thefreedictionary.com/Change+Agent ]

I like "historymaker"

one that by acts, ideas, or existence modifies the course of history

or history-maker

A person who influences the course of history or does something spectacular or worthy of remembrance.

Perhaps a good title that meets your "Lofty, grandiose" request would be Fate Shifter or Fate Maker.

I like these titles because fate is commonly regarded as being out of our control.

fate

a power that is believed to control what happens in the future

the things that will happen to a person or thing : the future that someone or something will have

The word you are looking for is

disrupter
a company that changes the traditional way an industry operates, especially in a new and effective way:
If customers talk to everybody else they get the status quo. We're the innovator; we're the disruptor.

Cambridge Dictionary

• Gates was always more accustomed to being a disruptor than being disrupted.

• Colin Dunlap: Neild on defense – as always. Some people have no idea exactly how good this guy is, even when he doesn't make tackles, because he is such a disruptor. And, something tells me Noel Devine will have a big game.

• They will be joining other speakers including John Doerr, Michael Moritz, Barry Diller, Zynga’s Mark Pincus, HP’s Todd Bradley, Google’s Marissa Mayer, Microsoft’s Yusuf Mehdi, and Twitter’s Jason Goldman.
  Cook, of course, started out as a disruptor himself in the 1980s when he brought accounting software to PCs. (TechCrunch)

I have three suggestions.

Luminary a person who sheds light on some subject or enlightens mankind; famous intellectual any well-known or celebrated person

Eminent : exhibiting eminence especially in standing above others in some quality or position : PROMINENT 2 : standing out so as to be readily perceived or noted : CONSPICUOUS 3 : jutting out : PROJECTING

Megastar A celebrity. Originally coined for a very famous or successful celebrity but now routinely used to describe anyone who has public exposure.

I'm here a little late! Got here searching for the same answer.

There's a pretty big gap in the language around this idea, but I finally landed on a word I was satisfied with. That word was Determinant.

I hope this helps, either you or those who come after me!