Here is some information on the Orc Hero's.

::Hero::	::Brief Description::
	This hero truly is the master of the blade. He is probably the best unit for assaulting enemy mining/wood units and his abilities, when used properly, make him extremely difficult to kill. Because you rarely need to resurrect him, the Blade Master continues gaining levels without being hindered.
	The Farseer is one of the best magic users in the game. He also makes a great scout early in a match by using Far Sight. Try and keep him protected and make full use of his abilities whenever possible. Build up levels quickly if you want to 'Level' towns, and town defenses with Earthquake.
	The Chieftain is another 'difficult to kill' Orc hero who is primarily good for wearing down and stunning groups of enemy units using Shock Wave and/or War Stomp. They are also good for keeping your units 'charged up' for combat situations when they have Endurance Aura. The Chaiftain is good as a support unit and can take a lot of hits, making him a good pointman; but tends to be a 'slow killer'.

Note: Pictures and information courtesy of Warcraft 3 Strategy.