A ‘t Hooft-Polyakov monopole in a dark sector is a viable dark-matter candidate as it is stable due to its topological charge. If the spontaneous symmetry breaking proceeds via the first order phase transition, monopoles can be produced from the collisions of expanding bubbles. In the case with a Coleman-Weinberg potential, a monopole with mass of O(10^{10}) GeV can explain the observed DM density. Interestingly, this is within a viable window for the PQ-symmetry breaking. Motivated by the coincidence of the energy scales, we have pursued a possibility of unifying the PQ symmetry breaking and the production of the monopole DM. Even simple models lead to interesting phenomena in cosmological history, like the Witten effect on the axion in the presence of the monopoles, the Lazarides-Shafi mechanism to avoid the domain wall problem, and the formation of Alice strings. I will explain these effects in a KSVZ-type axion model as well as a DFSZ-type axion model and will show how the cosmological domain wall problem of the axion models is avoided by these effects.