Studio Pierrot is a Japanese anime production studio mainly known for shonen manga adaptations. They currently create the famous shonen anime Naruto, and its spin-off. They also produced the Bleach anime in both of its phases, from 2009 to 2021 and then from 2022 onwards. Before the 2000s, they were best known for their Magical Girl series, such as Magical Angel Creamy Mami, Persia the Magic Fairy, Magical Star Magical Emi, Magical Idol Pastel Yumi, and Magical Stage Fancy Lala. They're also known for -among others- Dallos; the first OVA, Saber Rider and the Star Sheriffs, Yu Yu Hakusho, The Sonic The Hedgehog OVA and the Di C co-produced series The Mysterious Cities of Gold.
For a more complete listing, check out their ANN entry.
They also have a bit of a Never Live It Down streak regarding their handling of their shonen series' relationships, particularly in regards to shipping.