http://www.youtube.com/watch?v=DYYJlyoR2IY

The above is an excellent 2007 Finnish documentary "Mannerheim: General of the Czar, Marshal of Finland" with English subtitles on Field Marshall Gustav Mannerheim (1867-1951) which focuses for much of its coverage on Mannerheim's Imperial Russian service (4 decades). It gives rare materials and pictures on his personal life, quotes from his contemporary letters (personal) and modern views of Mannerheim. Mannerheim rose to the rank of Lieutenant General in the Russian army. A little spartan on details though covering specifically WWI: NO WWI units referred to except his divisional command in 1915 when he was promoted to Major-General. Highly recommended.
John
Toronto