My dear King Eric (what am I to do with you?)

I never knew Eric could command such a presence in class. He has his gang of ready followers at his beck and call. "Teacher, please leave us alone.. I am trying to sleep.." The class laughs at every comment he makes. They seem to respect him (far too much for my liking). I tried having English games in class, talk about world affairs, talk about their own lives, and basically try to make English as fun as possible without adhering so rigidly to the textbook (which they really hated). But once Eric shuts down (puts his head on the table and sleeps), others follow suit or just end up talking to one another and the English lesson becomes a fruitless exercise. It took me two months before slowly about two-thirds of the class started to pay attention (probably they knew I was trying very hard) but Eric still commanded attention.
Do I just ignore the boy? How can I? He is a student of mine.. How do I engage him? What can be done so that he gets enthused and the whole class gets enthused? A comment made by another student about Eric motivated me one day. 'He loves animals.. absolutely adores them.' That was a signal for me. Luckily, the whole class liked animals and most of them had pets at home.My English lessons (still taught with generic language skills in mind) moved towards content on animals. The class and I explored all sorts of issues pertaining to animals and the next two months were great. Eric (the king) absolutely loved the lessons and the enthusiasm he brought to class had the same spillover effects to his mates just as his negativity had in previous months. But then he grew listless as May approached, and then for two weeks, he did not turn up in school. It soon dawned on me that his problems may not be school-related at all but I had realised this too late...