So I'm crafting my own world, I added big events that shaped the world, a lot of it is generic but some of it has been changed. I wanna know is how to introduce it to the players. Stuff like the mind flayer empire was wiped out and nothing exist of their golden age, or better how do I treat historical figures? An old lich king from long ago, a long live red dragon sleeping under a mountain, or a angel who has prophecy his own return, how does the world treat this knowledge? Do commoners just know vague tales of this character or is it no one remember who exactly but more of the actions this figure did? Also what do the players know of this person? What is your advice? 

Well, the first thing to remember is: though you are excited about your world's rich history (and it can give your world lots of background flavor) most players will probably not care about many details that don't directly affect them. So they should MOSTLY be introduced to  aspects of history when it is relevant to them and the mission you are sending them on.

But for background color, you can drop bits of history into your mission description/intro, even if it isn't directly related.  'Back in the glory days of the Mind Flayer Empire, when the evil lich king Steve was still on the throne of Deadville, a group of wizards decided to create the world's largest hamster ball with which to capture the hamster demon Fluffsy..." 

They can find ruins and relics of the old days...instead of just a sword +1, make it a sword+1 etched with the runes of the Lich King's personal bodyguards.  Or a magic cloak with embroidery in the style of the Mind Flayer Empire.

NPCs can make historical references on the side. "Whew did ya feel that earth tremor? The dragon under the mountain musta rolled over, hee hee!"   A bard stands in a square calling out, "Gather round, and hear the epic ballad of the angel's prophecy! All contributions gratefully accepted..." (Have an expository ballad written, or at least a description, just in case they stop to listen!) Or maybe see a street theater troupe re-enacting the fall of the mind flayer empire as they wander into a new town.

Nice, I like your thinking that was helpful. Any other suggestion are appreciated 

Outside of direct exposition by various NPCs, you can also try to make nudge your PCs into asking about these kinds of things by naming prominent landmarks after historical figures.  Also keep in mind that one way to pique the players' curiosity is to make something a secret tied to NPCs that they care about.

If there are plot specific events, figures, entities, those can be introduced pretty organically. Historical entities change the world. Institutions, in particular, persist--for a real world example the pope is the pontifex maximus, a title that predates even the Roman Republic. States have fallen but that institution is still around. There are also cultural dialogues that leave their mark in a number of ways. NPC's, plot specific archive/records/library checks, the aforementioned institutions, etc can be a really good way to do this. Also, your plot has a lot to do with this, what's the trajectory of the current campaign, what's the barebones narrative here?

DM and historian here so this stuff might be unnecessarily pedantic or academic. 

Hello Fakinguy.  

the most important thing in History is that all history is written by the winners. and that it changes by everyones viewpoint. 
 some things to think of:

1) 1 area might know of a prophecy that other areas dont know.
2) the same event in history can be told differently by two people  e.g the town of applesberry know of cleansing of their people by the village or pearorange, while the pearoragnese claim that it was the applesberry folk tyrant who blamed the pearorange to lay claim to their land. it would be up to the party to figure out and decide the truth
3) commoners often know what their lords and priests tell them.  for better information the characters should tlak to the clergy or nobilty
4) you can slowly introduce it to them as quests. e.g a landless noble wishes them to retrive his estate that was part of his family dating back to the mind flayer empire . 

Hope this helps

I'd like to add that folk knowledge can maintain a very different narrative than the ruling powers. So bear that in mind when dealing with common npcs.

Before the campaign, you can send them a short gazetteer with the broad strokes and major figures, but keep it not-too-detailed. In the U.S., for example, we all know who George Washington was, but not many people know the name of his lieutenants; there's been 45 presidents, and most people can probably name the most recent ones, and a few older ones who've had major impacts, but couldn't name all of them. Probably similar to the rulers of your world. So give them those recent and big names. Keeping some things vague also gives you room to insert someone later if you need.

Also don't be afraid to include some incorrect information, especially if its plot-sensitive. People might popularly believe one thing, even though its not accurate. Heroes with undeserved reputations, discoveries attributed to the wrong person. Villains who've gotten a bad rap.

As people said, if its fun for you to build this detailed world, go for it, but don't assume your players will really care too much. And don't confuse setting with plot. The story you all create going forward will keep them interested in the campaign, not the events of a thousand years ago.