He is referred to as Ichi (one) but is the fourth son. He is very honest and very strong. In "Osomatsu-kun Grows Up" he has become a company president after marrying his predecessor's daughter. His name comes from Ichimatsumoyō (市松模様?), the Japanese word for check pattern.
In Osomatsu-san, he is the pessimist of the group and tends to overreact the most when it comes to being teased. He also has an affinity for cats.