What does it mean to be a person constantly translated into data? In platform ecosystems shaped by Alphabet, Meta, Amazon, Apple, and Microsoft, everyday life unfolds through infrastructures that do more than monitor behavior: they shape perception, choice, and self-understanding. Combining critical theory, cultural analysis, and media ethnography, this dissertation examines how surveillance cultures turn lived experience into computable traces and return them as if they reveal who we truly are. This process produces the data subject: a subject formed through datafication, for whom prediction feels like relevance, responsiveness feels like freedom, and participation becomes inseparable from extraction. Moving between conspiracy communities and the Fediverse, the dissertation traces how the data subject is intensified, lived, and sometimes unsettled. It shows how Big Tech captures distrust, irony, and intimacy, while also identifying moments where these conditions become visible, contestable, and open to infrastructural struggle.