Leadership has traditionally been viewed as an individual attribute that goes beyond management. All managers are expected to be leaders, but not all leaders have expertise in the management functions.
However, leaders may emerge without formal appointment. These leaders become influential either because they have special skills or resources that meet the needs of others or because the formally-appointed manager lacks leadership skills and the informal leader steps in to fill the vacuum. Provided the informal leader is supporting the goals of the organization, this can be a useful support to the manager.
“Managers are people who do things right and leaders are people who do the right things.” Warren G. Bennis