Lion

The Lion is a well-known and widespread symbol. This noble beast is the most represented animal in visual arts, sometimes a symbol of majesty and power, courage and justice, sometimes a mark of royalty, sometimes an astrological symbol.
The Hindu name for Leo is Simha, which word is said to be powerful in its utterance. Narasimha, a half man (nara) and half lion (simha),  is the fourth incarnation or avatar of Vishnu. Lord Vishnu appeared in a divine human form with a lion face to protect his devotee and to stop religiousness. Lion-headed Sarabeswara and Prathiyankara Devi are also worshiped as the savior against evils.
Certainly, the lion personifies the big protecting force. Sphinx or the Egyptian goddess of war Sekhmet, with a lion head, or Mithra, the Sun god of Persia, with a lion face, the Assyrian Gate Guardians of Babylon or the Etruscan lion with wings at the entrance of the Temple mountain at Troy are well known examples for this. Ancient Egyptians believed that the eye of the sun was the great lion-form of Shu.

 In Hindu cosmology, Simha also is the emblem of the solar cycle, representing the life and duration of the sun. Thus, we see a meant parallel between the sun as the heart of the solar system and the lion who rules the human heart. Probably, it is a symbol of connection between the spiritual sun to the spiritual heart of man.
In Islamic tradition, this motif is also popular. For example, the Lion and Sun is one of the main emblems of Iran. In religious context, the qualities of bravery, strength, and valor of lion is mentioned in the Koran, the traditions of the Prophet.
In Christianity, the Lion is one of the four living creatures described around the throne of the Almighty and they are chosen as symbols of the four evangelists. Mark is traditionally represented by the Lion.

There is a interesting idea that the lion is rumored to sleep with one eye open. In that case he always is ready to wake up and to spark the fire to shine the way of the human soul to the final victory, to the Sun.