Then: Ioan Gruffudd
Now: Miles Teller
Age: Gruffudd originated the part of Dr. Reed Richards when he was 31. At age 27, Teller is a little younger.
Pedigree: Gruffudd had a number of roles before he starred in Fantastic Four, but none super notable. Miles Teller has been all over the genres, appearing in Footloose, 21 & Over, The Spectacular Now, That Awkward Moment, and the upcoming YA adaptation, Divergent. It's safe to say he can tackle action, too.