Panchmukhi is a sanskrit word which when translated literally means, one having 5 faces. Lord Hanuman appeared in his Panchmukhi Hanuman avatar during the epic battle of Lord ram with Ravan. As the story goes, during the battle Ravan was being aided by the king of Patal-lok (underworld), Mahiravana. Mahiravana took the form of Vibhishan, abducted Lord ram and lakshman and held them prisoners in the Patal-lok.
When Hanuman came to know about this, he entered the Patal-lok with the purpose of rescuing them. During his quest, he discovered that Mahiravana's life was contained in five lamps. Extinguish them and he dies. There was only one catch; all the lamps were kept in different directions and had to be extinguished together for him to die. To accomplish this and kill Mahiravana, Lord Hanuman then took the avatar of Panchmukhi Hanuman.
Hayagriva (the horse face) – His upwards facing form help people in generating goodwill. His devotees will always achieve what they aim for and will always be in the company of the learned. They will have good children and attain salvation. narasimha (the lion face) He faces south and banishes all kinds of fears, sins and evils.