Ludwig Frankenstein made a monster using the Silver Surfer as a model and duplicated all of the Surfer's powers onto an empty body. The result was a murderous slave with the Power Cosmic and his own silver surfboard.
After devastating Earth and terrorising Frankenstein's enemies, Frankensurfer was defeated by the real Silver Surfer.
Frankensurfer was created by Stan Lee and John Buscema and his only appearance was in The Silver Surfer (1968) #7
Frankensurfer, despite being a clone of the Silver Surfer, shares all his powers including the Power Cosmic. In terms of strength and power, the two were equal - the only difference was the real Surfer's humanity.