The Leader is sufficiently stronger than regular Cybermen. When attacked with gold, Cyber-Leaders are more resistant. They are designated as the Leader by a black helmet or black handle bars on their helmet.
The Cybermen from Pete's World did not designate a Cyber-Leader until they invaded this universe in 2007. The Leader could be identified by black handle bars. When he was destroyed, the information he had was downloaded into another Cyberman, who became the new Cyber-Leader. In The Next Doctor the Cyber leader has a visible head casing, showing it's Human / cybernetic brain. Also on this design there are more black commponets on the cyberleader's head, were as the previous one only had black handel bars.
The Cyber-Leaders have appeared in the episodes...