  We show generalized Galileons -- a particular subclass of Horndeski gravity
-- arise from a consistent Kaluza-Klein reduction of the low-energy effective
action of heterotic string theory to first order in $\alpha'$. This suggests
Horndeski theories of gravity have a string-theoretic origin. The form of the
Galileonic terms is precisely fixed by parameters of the embedding spacetime,
so that only a specific subset of Horndeski theories is permitted by string
theory. A novel limit of the model is considered by performing a dimensionful
rescaling of $\alpha'$.
