What was the name of the first American lunar orbiter?

The first American lunar orbiter was Lunar Orbiter 1.

NASA launched Lunar Orbiter 1 on August 10, 1966, as the first mission in the Lunar Orbiter program. Its main purpose was to photograph possible landing sites for the upcoming Surveyor and Apollo missions, helping engineers identify relatively smooth and safe terrain. It entered lunar orbit on August 14.

The spacecraft returned high- and medium-resolution photographs covering more than 5 million square kilometers of the Moon. It also transmitted two early images of Earth from lunar distance, making the mission important beyond its practical landing-site role. Its camera system developed film aboard the spacecraft and scanned the images for radio transmission to Earth.

Lunar Orbiter 1 is easy to confuse with Surveyor 1, which was the first American soft lander on the Moon, or Ranger 7, which photographed the lunar surface before impact. Apollo 8 was the first crewed spacecraft to orbit the Moon, but it was not an orbiter in this robotic program.