We give an overview of the Hopf algebraic approach to renormalization, with a focus on gauge theories. We illustrate this with Kreimer's gauge theory theorem from 2006 and sketch a proof. It relates Hopf ideals generated by Slavnov-Taylor identities to the Hochschild cocycles that are given by grafting operators.
In the second part of the talk I will briefly present Kreimer's unexpected influence on noncommutative geometry via my more recent research. In joint work with Teun van Nuland we uncover a rich structure of the spectral action functional. We express its Taylor expansion in an inner perturbation in terms of Yang-Mills and Chern-Simons forms integrated against even Hochschild and odd cyclic cocycles, respectively.