Iruka became a teacher after being injured while on mission lead by Kakashi Hatake. Recognizing his heart and compassion might end up injuring himself or others, Iruka decided to retire from field work and become a teacher.

Iruka is  both big-hearted, and soft-hearted. This is most often seen through his teaching methods, often keeping a watchful eye over his students as they progress. This however, does not mean that he is a pushover, as he can be stern when the situation calls for it, most often seen when he shouts at his students in order to get them to obey him.