Introducing a character later in a bookseries

Im halfway through writing a trilogy. Ive written down half of the second novel. Ive told myself to finish all three before going into editing; i just want the whole story written down first so i can easily go back and edit some holes away i may create along the way.

Now my question. The childhood friend of my main characters barely plays any role in the first book (He is mentioned throughout and only appears in the last chapter, as the story takes place in another world). However, he gets a major role and POV chapters in the second and third books.

Should I try to establish his character more in the first book? Or is it fine to have him far in the background in the first. I was thinking of writing him into the very first chapter, but i think it will make the book start slower, as my current first chapter is a nice dynamic start.

Advice is nice :)