We formulate the Hopf algebraic approach of Connes and Kreimer to
renormalization in perturbative quantum field theory using triangular matrix
representation. We give a Rota-Baxter anti-homomorphism from general
regularized functionals on the Feynman graph Hopf algebra to triangular
matrices with entries in a Rota-Baxter algebra. For characters mapping to the
group of unipotent triangular matrices we derive the algebraic Birkhoff
decomposition for matrices using Spitzer's identity. This simple matrix
factorization is applied to characterize and calculate perturbative
renormalization.