Paech was a biochemist and an ecologist, as well as an ardent believer in the beauty of nature. Upon being forcefully recruited to Zero Dawn, Paech was furious to learn the true nature of the Faro Plague and their creation at the hands of Faro Automated Solutions, especially its founder Ted Faro.
Initially, Paech was skeptical of Zero Dawn and the purpose of ARTEMIS, as he believed that humanity was too irresponsible to rebuild Earth's biosphere. However, he was convinced otherwise by his fellow ecologist and later partner Charles Ronson. Once Paech finished his task, he opted for medical euthanasia rather than living out his remaining life in Elysium, which he distastefully saw it as claustrophobic.
Paech made a promise with Ronson that he would be with him during his last moments of life. Unfortunately, due to the Faro Swarm's rapid advance, Ronson was forced to choose between preserving several samples of Paradisaea zygotes, or attending Tom Paech's euthanasia as he had promised. Under stress, Ronson chose to save the samples and Paech died alone.