Louis XIII, or Louis the Just, displayed great courage on the battlefield and his military might was one of the defining characteristics of his reign. (See France: Recent Military History). Additionally, in reality he was a fairly mentally unstable man due to the abuse inflicted by his mother at an early age. He stammered and was chronically ill. These aspects are not included in our production (or, indeed, in the novel).
From what I can tell, Louis was a lonely man. He was frequently betrayed by people he held close to him, such as his favorites de Luynes and Cinq-Mars, and had to execute or exile them because they threatened his state. His relations with his mother never improved, though he was "reconciled" to her by Cardinal Richelieu, and his marriage was not a particularly happy one, especially once Richelieu threw suspicion on Anne as a possible conspirator against the crown.
Louis took solace in his military campaigns and at the time of his death (aged 41, of tuberculosis) was "respected as one of the most powerful monarchs in Europe".