Order: New to the old.

Take this from danbooru, so credits to whoever put this information.
An employee of Nitroplus. He has two different nicknames to separate commercial work from doujinshi.
Circle: パンダニク (Panda-Niku). The other main circle member is やきにくATK (Yakiniku ATK).
Often confused with said circle member, なまにくATK (Namaniku ATK), in commercial work crediting.

Name used for commercial artwork (Nitroplus): 大熊猫介 (Ookuma Nekosuke)
Name used for fan artwork / doujinshi (Panda-Niku): JCパンダム (J.C. Pandam)

Pixiv (Nitroplus): http://www.pixiv.net/member.php?id=36377
Pixiv (Panda-Niku): http://www.pixiv.net/member.php?id=5372574
Twitter (Nitroplus): http://twitter.com/panda_ookuma
Twitter (Panda-Niku): https://twitter.com/jc_pandam