The article describes the achievements of Martti Ahtisaari as a politician, especially as a mediator in international conflicts, an activity for which he was awarded the Nobel Peace Prize in 2008. The author presents Ahtisaari's involvement in the peace building process on three continents - with special attention on his work in Namibia, Indonesia and Kosovo. The negotiator's connections with intergovernmental and non-governmental institutions are underscored. The politician's activity as president of Finland is also highlighted in the aspect of his views on European integration. Additionally, the necessary qualities of a negotiator are discussed. The author makes ample use of Ahtisaari's own writings.