A devaputta who visited the Buddha and told him that the path of the Ariyan disciples was hard to follow and their goal hard to win. The Buddha pointed out to him that the difficult thing had been and was being accomplished (S.i.48).
The Commentary (SA.i.83) explains that Kāmada had been a yogāvacara on earth, but had died before he could attain to any Fruits of the Path and that here he laments his disappointment.