More than any other skill, or trait, or quality, emotional intelligence is key in leadership.
I'll start with my own history: In my early twenties I was a manager at a very busy, very strict, training store McDonald's. I mention this as it was the first place I got any real leadership experience. More recently I have worked at a university bar and restaurant, and although I have not taken any managerial positions there, I have had the opportunity to work with an amazing team of very social people who have taught me a lot about relationship building in general.
This recent environment has allowed me to compare organizational styles as well as managerial styles: McDonald's being operations oriented, while the bar being relations oriented. It's given me a lot to think about in terms of interacting with people, management, and more importantly leadership.
While working at the bar, I was also attending public lectures held by the Peter Lougheed Leadership College. They were hosted in particular by the right honorable (former prime minister of Canada) Kim Campbell, who used the networks she'd cultivated over the years to bring in amazing speakers with demonstrated real world leadership experience. The one claim every speaker made independent of each other, regardless of background or diversity of experience, was that emotional intelligence is key.
After hearing the stories of others, as well as reflecting on my own experiences, I have come to conclusion that it really is about emotional intelligence. At the end of the day, business is about people, be it customers, clients, coworkers or colleagues: Being able to navigate our emotional interactions within the larger context of a complex social world is the foundation to any lasting relationship.