Giant Drill-Beaked Bird

It's a large bird, which has a number of body piercings and Rinnegan, implying it is being controlled by Pain.

Appearance
The bird itself is unusual, as not only does it demonstrate a prominent and jagged beak, but it also features three distinct legs (and wings in the manga).

Abilities
This summon can move at an incredibly fast speed, and can use that velocity combined with its beak to form powerful dive attacks. In the anime, the bird had additional abilities where it could lay a large quantity of eggs, that subsequently explode like bombs and while flying low over Konoha produced dust clouds strewn with lightning in its wake.

Itachi Pursuit Arc
It is summoned briefly during Pain's fight with Jiraiya.

Invasion of Pain Arc
He is summoned again to attack Naruto after he uses his perfected Rasenshuriken.

Shinobi World War Arc
The bird is next summoned by the revived Pain along with the Giant Multi-Headed Dog to provide a way for Nagato to move. Itachi soon retreats to the top of the birds head alongside Nagato. Later, after Itachi is freed from Kabuto's control, he uses Amaterasu on both Nagato and the giant bird, incapacitating it.