What do you call that first encounter which has made a tremendous impact in your life?

I'm trying to think of a word which can describe a first encounter that has made a tremendous impact in my life. Unfortunately, I can't think of one. Is there a word to describe such an event?

The first word that came to me was pivotal:

[Merriam-Webster]

1 : of, relating to, or constituting a pivot
2 : vitally important : CRITICAL

// She is at a pivotal point in her career.
// the report was missing a pivotal piece of information

Generally speaking, it combines both of the above senses. So not only is something vitally important but it also serves as a turning point.

You can look back on an event in your life that had a significant impact, without which things would obviously have turned out differently for you:

It was a pivotal event.

You could similarly say:

It was a key moment.

turning-point

the time at which a situation starts to change in an important way

Source: Cambridge Dicionary