One could argue that leadership is the art of getting work done through others. How is that accomplished? By being skilled in the art of influence. Influence is the ability to have a positive impact on others, persuading or convincing others in order to gain their support.
We make most decisions not with our cognitive capability but with our emotions. Mastering emotions will thus make you more capable of influencing others. Emotional intelligence is the ability to recognise your own emotions and those of others. And to be able to manage and influence your own emotions and those of others.