U kind found this a little broad, and I don't see too many dates, so mine as well put down my initial thoughts.
As soon as I read this, I thought of the Last and First Men, a science fiction novel by Olaf Stapleton.
When speaking of the only two, true, and meaningful prohets to humanity, he stated that Socrates and Jesus were these people.
Although many may argue the validity of that statement, and it was indeed written as part of a ficticious work, I still believe it calls to light two very important, and influential people since the birth of western civilization.
Benjamin Franklin for his work in electricity?
The Elightenment period that forged a modern democratic ethos?
The fall of Rome?
As for earlier and more basic events, I would imagine the extinction/assimilation of Neandertals would be fairly important, being it made Homo Sapien the dominant bipedal mammal on earth.