This is a knight of the "Order of the Hospital of St John of Jerusalem", also known as a Hospitaller, who fought in the Crusades.

Interestingly, Sean Connery acted as King Richard, who returns from the Crusades and blesses the marriage of Robin and Marian in the 1991 movie "Robin Hood: Prince of Thieves".

The Crusader helmet was a flat-topped "pot helm", with a hinged visor covering the face, a standard headgear of Christian knights.

That is the coat of arms of the kingdom of Bohemia (present day Czech Republic). Hospitallers had black later red tunic with white cross..England had three golden lions on the red background.

The Hospitaller had two uniforms, one red with a white cross and one black with a white cross. However, knights belonging to these orders didn t always wear this uniforms, but their own family colours (similar to how Brian du Bois Gilbert does in Ivanhoe despite being a templar... this is accurate) and thus the knight here is wearing his family heraldry despite being a member of the hospitaller order. His coat of arms is fictional but most similar to Brockhorst or the Anglo-Norman Delavach.