My understanding is that they used to be driven by people with primarily economic issues with the euro, some economists. I don't think that that's really what I'd call extremism.
AfD was founded by Gauland, Bernd Lucke, and former members of the Christian Democratic Union of Germany (CDU) to oppose the policies of the Eurozone as a right-wing and moderately Eurosceptic alternative to the centre-right but pro-European CDU. The party presented itself as an economic liberal, soft Eurosceptic, and conservative movement in its early years. AfD has subsequently moved further to the right, and expanded its policies under successive leaderships to include opposition to immigration, Islam, and the European Union. Since 2015, AfD's ideology has been characterised by Islamophobia, anti-immigration, German nationalism, national-conservative, and Euroscepticism.
Yeah, WP doesn't describe the euro issue, but does talk about the shift.
Bernd Lucke (born 19 August 1962) is a German economist and politician. Lucke was elected a Member of the European Parliament (MEP) for the Alternative für Deutschland (AfD) in 2014.
Lucke lost the leadership of the AfD to Frauke Petry in July 2015. Petry's election was considered a shift of the party to extremist positions; Lucke subsequently left the party. In July 2015 he and other former AfD members founded the political party Liberal-Konservative Reformer (formerly Allianz für Fortschritt und Aufbruch, "Alliance for progress and renewal", abbreviated ALFA).
Also, that shot of Lucke reminds me of the MAD kid, Alfred E. Newman:
.jpg){kind=link}