Introducing characters is an art in itself.
I believe that a character should be described once, in a memorable and vivid way, and as early as the narrative allows. If you’ve done your job well, the reader develops an internal image, and unless it’s absolutely pertinent to the story, this should not be altered, tampered with, or even mentioned again (or it can pull the reader out of the story).
My approach is to introduce each character in a few lines, or preferably a single sentence, in a way that really cements the character in the reader’s mind. One of my writing buddies called this a Pen Portrait.