[itex]1/(4\pi\epsilon_0)[/itex] in SI units is equal to c^2, with factors of ten coming in in the conversion from cgs to MKS.T his comes from [itex]\epsilon_0\times \mu_0=1/c^2[/itex]. [itex]\mu_0[/itex] is not a fundamental constant, but just comes from
[itex]\mu_0/4\pi=10^{-7}[/itex] with the factor [itex]10^{-7}[/itex] coming from the different units. There is also a factor of ten due to the difference between the original absolute Ampere and the SI Ampere.
Historically, the c came as the ratio between the electric charge that was natural for the current in magnetic phenomena and the electric charge that occurred in electrostatic phenomena. In order to use only one charge, the factor c was introduced.