I have a question: What qualities define a great team leader? Thank you for your answer

You can find litterature in English about teams and leadership from Helmet-online catalogue (www.helmet.fi) for example by using keywords (in Finnish) tiimit and johtaminen and then limit the search by language (English). As a result you get, among others, Belbin, Meredith: Team roles at work 2010; Robbins, Stephen P: Essentials of organizational behavior 2010; Godard, Alain: Transformational leadership: shared dreams to succeed 2000; Goleman, Daniel: The new leaders: transforming the art of leadership into the science of results 2003.

Here is one internetpage dealing with the subject:
http://www.teams-and-leadership.com/