Merkel, 61, is the European Union's longest-serving head of government and has been a serial winner of Forbes magazine's title of world's most powerful woman. Merkel helped negotiate the Kyoto accord to curb greenhouse gas emissions as environment minister in the 1990s. In the crisis over Ukraine, she has stuck doggedly to efforts to keep the leaders of Russia and Ukraine talking in the face of repeated setbacks in implementing a peace accord, while also backing sanctions against Russia. Merkel has been a dominant figure in shaping Europe's response to the debt crisis that started unfolding in Greece six years ago and flared anew this year. [...] Merkel has stuck to her optimistic insistence that "we will manage it" and refused to name a limit to the number of people Germany can take in, despite mounting criticism from conservative allies.