The Celestial who appears at the end of Eternals is Arishem.
Arishem the Judge is the immense red Celestial who arrives after Sersi, Phastos, and Kingo help stop the Emergence of Tiamut. He takes the three Eternals into space and tells them that humanity will be judged by the memories they carry. Arishem’s appearance establishes that the Earth’s victory has not ended the larger cosmic conflict.
Earlier in the film, Arishem explains that Celestials plant seeds inside developing planets. The energy produced by intelligent life eventually allows a new Celestial to emerge, but that process destroys the host world. Earth’s seed is Tiamut, whose Emergence is halted when Sersi uses the Uni-Mind’s power to transform him into stone.
Arishem is not the Celestial born from Earth. That role belongs to Tiamut, while Eson the Searcher is a different Celestial shown in a flashback in Guardians of the Galaxy. The phrase “the Celestial” can therefore be misleading: Arishem is the judge and architect of the process, while Tiamut is the dormant being inside Earth. Arishem is voiced by David Kaye and is based on a Marvel Comics character created by Jack Kirby.