  We argue that the relevant higher gauge group for the non-abelian
generalization of the self-dual string equation is the string 2-group. We then
derive the corresponding equations of motion and discuss their properties. The
underlying geometric picture is a string structure, i.e. a categorified
principal bundle with connection whose structure 2-group is the string 2-group.
We readily write down the explicit elementary solution to our equations, which
is the categorified analogue of the 't Hooft-Polyakov monopole. Our solution
passes all the relevant consistency checks; in particular, it is globally
defined on $\mathbb{R}^4$ and approaches the abelian self-dual string of charge
one at infinity. We note that our equations also arise as the BPS equations in
a recently proposed six-dimensional superconformal field theory and we show
that with our choice of higher gauge structure, the action of this theory can
be reduced to four-dimensional supersymmetric Yang-Mills theory.
