Edit: Since A.C. has returned his study guide to the web, he has requested that the content on this page that was his be removed.
You can find his restored guide here: http://xenogearsxenosagastudyguide.blogspot.com/

You can find general information on Dmitri Yuriev elsewhere:
http://xenosaga.wikia.com/wiki/Dmitri_Yuriev