We propose a unified scalar field theory that modifies general relativity by intro-ducing a novel scalar boson coupling to matter, thereby altering the gravitationalinteraction at galactic and cosmological scales. The modified Einstein equations in-clude an additional term Φμν , representing the scalar field’s contribution to space-time curvature. This scalar boson, herein referred to as the Gravitational ScalarBoson (GSB), is hypothesized to possess a radially varying coupling strength α(r),enhancing its influence in regions where deviations from Newtonian gravity are ob-served, such as in galaxy rotation curves. We derive the theoretical foundationsof the model, discuss its implications for gravitational dynamics, and apply it tothe spiral galaxy NGC 3198 as a test case. The optimized coupling strength atr = 0, α0 = 0.254, aligns with theoretical expectations and complies with observa-tional constraints. Additionally, we explore the broader cosmological implications ofthe GSB, including its potential role in cosmic expansion and structure formation.Building upon this framework, we advance towards a unified theory by unifying allfundamental interactions and particles within this scalar field paradigm. Our resultssupport the potential of this unified scalar field theory, centered around the pro-posed GSB, as an alternative to dark matter in explaining galactic dynamics andoffer insights into a comprehensive unification of gravity with other fundamentalforces.