Katha Upanishad

The Self (atman) is the owner of the chariot;

the body (sarira) is the chariot;

intuitive discernment and awareness (buddhi) is the charioteer;

the thinking function (manas) is the bridle;

the sense forces (indriya) are the horses;

and the objects or spheres of sense perception (visaya) are the ranging ground. 

The individual in whom the Self, the sense forces and the mind are joined is called the eater or enjoyer (bhoktar).

For one who is devoid of real insight and has not properly and constantly yoked and tamed his mind – that is to say, for one who has not disciplined and controlled both his conscious mental faculty (manas) and the intuitive awareness (buddhi) which is a manifestation of the irrational unconscious – the sense forces become unmanageable, like the wicked horses of a charioteer.  But for him who is always full of intuitive awareness and who has tamed and yoked his mind, the senses are subdued like the good horses of a charioteer.

He who lacks the proper intuitive awareness and is thoughtless and impure, does not reach That Place [the state of transcendental existence] he tips over into the whirlpool of death and rebirth (samsara). 

But he who is full of intuitive awareness, thoughtful and pure at all times, reaches that place, whence one is not reborn.  The man who has for his charioteer intuitive awareness, and for his bridle the mind, attains the end of his journey – which is a great distance away.  That goal is the supreme abode of Visnu – the cosmic all pervading Self divine.