Who is Kemal Kilicdaroglu, a leading challenger to Erdogan in Turkey's election?

Kemal Kilicdaroglu, leader of the Republican People's Party and presidential candidate of the a broad opposition alliance, greets supporters at a rally while campaigning for the presidential election on April 27 in Tekirdag, Turkey. (Burak Kara/Getty Images)

ISTANBUL, Turkey — There's a big election coming up in Turkey on May 14, one that could shape the trajectory of this NATO ally for years to come.

President Recep Tayyip Erdogan, who has led the country for 20 years, is asking voters to grant him another five years in office.