Answer: Agreeableness.
Step-by-step explanation:
Agreeableness is one of the five factors of personality, known as Big Five. Other four traits include openness to experience, conscientiousness, extraversion and neuroticism. If someone is agreeable, it means that he/she is people-oriented, demonstrates good social skills, and attempts to find something positive in anyone he/she encounters.
Agreeableness best fits into the account of Istvan's personality we are given, because trustworthiness, consideration, compassion and loyalty are all component parts of this trait.