Short answers, pulled from the story.
Uddaka Rāmaputta was a sage and meditation teacher identified in Buddhist tradition as one of the last teachers of Gautama Buddha before his enlightenment. Gotama studied under him after leaving Āḷāra Kālāma, and Rāmaputta acknowledged Gotama as his superior, equal to his own predecessor Uddaka Rāma.
Uddaka Rāmaputta taught refined meditative states known as the jhāna formless attainments, or arūpa samāpatti. His lineage included the highest attainment called the sphere of neither perception nor non-perception, though Rāmaputta himself had not personally reached that level.
Gotama concluded that Uddaka Rāmaputta's method would not lead to complete enlightenment. Despite being offered sole leadership of Rāmaputta's community, he declined and resumed his wandering in search of a deeper path.
After his awakening, the Buddha first thought of Uddaka Rāmaputta as someone capable of understanding his Dhamma, but learned that Rāmaputta had already died by that time.
Uddaka Rāmaputta appears in the Ariyapariyesana Sutta (MN 26) of the Majjhima Nikaya, which scholars identify as the likely source of later Pali versions of the story. He is also mentioned across the four Nikayas, in the Vinaya, in commentaries to the Dhammapada, and in parallel Sanskrit and Chinese accounts including the Mahāvastu.
The scholar Andre Bareau argued he was a fictional creation, but later scholars have accepted the possibility that he was a real person. Sources from different early Buddhist schools all agree in placing Uddaka Rāmaputta in Rajagriha during the Buddha's lifetime, and the pilgrim Hsuan Tsang recorded traditions from his own era linking Rāmaputta to the same region.