Yui Haga (葉賀ユイ, Haga Yui) is a Japanese light novel, manga, and anime artist. His most famous work is Baka and Test, which inspired a two series anime and a video game for the PlayStation Portable. He is also responsible for Astarotte no Omocha! and Sakura*Nadeshiko. Additionally, he was responsible for the ending illustrations in Nisemonogatari.
Source: “Yui Haga”, English Wikipedia (CC BY-SA 4.0), excerpt