Yoshimura (吉村) is the elderly janitor of Kaimei High School. He often has a lot of work and sometimes asks the Sket Dan to help out.

Manga Debut: Chapter 1 (Paint-Mask)

Anime Debut: Episode 1 (The Campus SKET)

(source: http://sketdance.wikia.com/wiki/Yoshimura_%28janitor%29</a>)