Explaining who a character is?

I've been re-reading books from my favorite series and was wondering what others think when this happens:

In the 3rd or 4th book, the author brings in a character who played a not-insignificant role in previous books. The author then proceeds to explain who that character is and the role he or she has played in the series.

I find that this pulls me right out of the story...does anyone else feel the same or do you find it to be a helpful reminder?

Looking forward to hearing your thoughts!

Matt