Which fighter won the UFC 189 interim featherweight championship in 2015?

Conor McGregor won the UFC 189 interim featherweight championship in 2015.

McGregor faced Chad Mendes in the main event at the MGM Grand Garden Arena in Las Vegas on July 11, 2015. Mendes used wrestling effectively early, but McGregor rallied and won by technical knockout in the second round. The victory made McGregor the interim UFC featherweight champion.

The interim title was created because the undisputed champion, José Aldo, was unable to compete at the scheduled event. McGregor later unified the titles by defeating Aldo at UFC 194 in December 2015, finishing him in 13 seconds.

UFC 189 is therefore distinct from UFC 194. McGregor won an interim championship against Mendes at UFC 189, then won the undisputed featherweight title against Aldo at the later event.