Erdoğan had been in prison and had a political ban.

In Turkey a political ban means you can't get elected, but it does not stop you from being the leader of a political party. In the 2002 elections Erdoğan was very much the face of the party and the campaign. He was the man. But he wasn't allowed to run for PM, so the party ran with a proxy instead. That proxy PM served only long enough to lift Erdoğan's ban and do some fucked up retroactive election bullshittery to get Erdoğan officially elected as a representative in the parliament months after the general elections. The main opposition, in their infinite wisdom, helped them cook up a bullshit reason to do a repeat of the last general election in a small town, and allowed Erdoğan to run in place of another rep that had been in those same ballots earlier. The proxy PM then resigned and left his seat to Erdoğan, who was now an officially elected representative.