[Moved from related topic, Tintin and Alph-art: storyline - general discussion
I'm not too convinced Akass is Rastapopoulos, either - why wouldn't Tintin recognise his voice ? They've met enough, and Tintin didn't see him that long ago ("The Red Sea Sharks" being the last time, as he wasn't aware they'd met in "Flight 714", of course), so he would surely have recognised his voice. The sketches at the end of the 2004 edition echo this - Hergé wrote "Rastapopoulos ?" around sketches of Akass, but an Akass looking notably different from how he's pictured in the rest of the book (shape of nose and chin). Hergé himself wasn't sure, and subsequently I'm not convinced either, Kirthi.
So here's my guess - how about Omar Ben Salaad, the head of the drug-trafficking ring in "The Crab With The Golden Claws" ? He's got the right shape of nose, same sort of build, Tintin has met him before, but not seen him for a long time, hence his inability to recognise him ("That voice ... Some of his inotations remind me of ... of ... someone. But who ?"). Plus he's been out of the picture for quite some time, so he's had plenty of time to set up the art forgery business.