We provide a computer-assisted proof of one of the central open questions in one-dimensional renormalization theory - universality of the golden-mean Siegel disks. We further show that for every function in the stable manifold of the golden-mean renormalization fxed point the boundary of the Siegel disk is a quasicircle which coincides with the closure of the critical orbit, and that the dynamics on the boundary of the Siegel disk is rigid. Furthermore, we extend the renormalization from one-dimensional analytic maps with a golden-mean Siegel disk to two-dimensional dissi-pative He acute accent non-like maps and show that the renormalization hyperbolicity result still holds in this setting.