Koxinga, importantly, was mentally unstable, known to have a vicious temper and tendency towards ordering executions. While this might be explained by the trauma of his family being killed by the Qing army and his mother's reported suicide (in order to prevent capture by the Qing), it was also speculated that he suffered from syphilis, a suspicion held by a Dutch doctor, Christian Beyer, who treated him. Vittorio Riccio noted that Koxinga held samurai ideals on bravery, used "feigned and hearty laughter" to show anger, and adhered to bushido because of his samurai training and his Japanese upbringing. One Spanish missionary proffered a personal opinion that his bad temper and reported propensity for violence was due to Japanese heritage; however, this same missionary's account of the number of Koxinga's executions was greatly exaggerated.