Screenwriting : Character introductions by Brian Stoneking

I would say around half way through. I'm big on surprises and unexpected turns in stories, and new characters always introduce something fresh when they enter. By the halfway mark, you still have plenty of time to create a real and vibrant character. Any introductions past the half-way mark might feel rushed or forced.

The final page. If it happens after that, something has gone horribly wrong.

When they first appear on film and like CJ said by the final page.

Introduce them as they become relevant to the story. We should probably know who we're following, what they want, and why they can't get it by page 10 though.

Wherever the story needs them to be introduced. :)

ASAP or whenever they first show up in the story. The audience needs to who they are and why they are there at that time.

The sooner the better. I try to introduce all my main characters by the first ten pages. I figure that's as far as an industry professional will go before deciding whether or not the rest of my screenplay is worth reading. Of course, that assumes my first three pages don't suck!

I hate that word "should".

An intro should be complete in a line or two. Then we learn about the person for the rest of the screenplay.

Sooner the better, I like Allen's style with this...narrating his characters entry so he saves us time we can focus on the story...

Isn't a lot going to depend on what type of script it is and what type of story it is? It's not uncommon for TV pilot scripts to introduce a 'puppet master' type of season/series antagonist towards the end. Some movie scripts will do this too if it's intended as a series or franchise (for example, Thanos isn't seen until the dying moments of The Avengers).

Yeah, I think some people have missed the question completely. It's perfectly plausible that a character, even a significant one, could first appear in the final moments of a script. To try and set a deadline to introduce everyone is an unnecessary rule.

I try to introduce the main characters as early as possible. However, the story dictates when they first appear on film, which is when they are first introduced.

"At what page"? Before the last page. A character is introduced as it is needed by the storyline - no sooner & no later.

What CJ Walley said. That's not a rule worth following.

There isn't a set rule for this so it is what works best for your story. The Wizard of Oz didn't introduce the Wizard until the end of the movie : )

It depends on several factors story, length and number of characters.

When their presence is necessary to the plot, which might include foreshadowing events that will eventually happen.