Voice of Light

The giant halo that appeared on the Warrior's Peak of Planet O-50 is a sentient force who bestowed Gai Kurenai with the ability to transform into Ultraman Orb. Although its true name is unknown, the final episode of Ultraman Orb: The Chronicle refers to them as the voice of light (光の声).

Ultraman Orb THE ORIGIN SAGA
The giant halo was prophesied to grant the chosen one with the power of Ultraman Orb. To do this, they would accept the challenge of climbing the unexplored Warrior's Peak in the O-50. Two members of the defense force, Gai and Jugglus Juggler would race themselves to the peak. Although Juggler arrived first, he was quickly rejected and chooses Gai instead. The giant halo in turn assimilated with Gai and transform into Ultraman Orb (Origin the First).

The first mission that it granted was to stop the threat of Bezelbs from spreading Kugutsu across the galaxy. After completing the task, Ultraman Orb was further evolved into Orb Origin.

Ultraman Orb Chronicle: Chapters 2 & 3
With his next mission, Gai was ordered to collect all four elemental jewels that would make up the additional powers of Orbcalibur. Although he succeeded, the giant halo was initially unresponsive before Gai thwarted the prison break on Planet 484. It provided Gai with the Orb Ring, an object which allows him to manifest the powers of past Ultra Warriors through his forms and the mission to stop Maga-Orochi's awakening on Earth.

Ultraman Orb: The Chronicle
During Gai's return to Warrior's Peak, the giant halo emerged from the Orb Ring and discussed with Gai of the new Ultra Warriors Ultraman Rosso and Ultraman Blu. Gai assured the ring that his bonds with his comrades is what giving him the strength to move on before departing alone.

Trivia

 * Because of their shared voice actor, the voice of light is suspected to be the Orb Ring itself and is implied to have followed Gai during his time on Earth.