John Gauden & King of England Charles I 
Eikon Basilike [EPUB ebook] 
The Pourtracture of His Sacred Majestie, in His Solitudes and Sufferings

This is a very important book, because it helped to develop and sustain the image of Charles I as a martyr, who was misunderstood and wrongly beheaded. It was in print on the day of his execution and became a best-seller. Many believe that it was co-authored by Gauden (Bishop of Worcester) and Charles I himself.