what is the name of deomon/demoness in Ramayana who has no proper body but only stomach and two eyes in the stomach and what role did he play?

The demon you are looking for is Kabandha. He advises Rama to form an alliance with Sugriva, who would be of assistance in the search for Rama's wife Sita, who had been kidnapped by Ravana, the demon-king of Lanka. Following Kabandha's instructions, Rama befriends Sugriva and rescues Sita with his help.