In the mid 1980's I read a book that had a plot that went like this:
A solder who was near death was saved by his scientist/professor friend. Unbeknown to the soldier, the scientist made some amazing changes to his body, giving him powers that would be activated if he ever visited an alien planet.
The scientist had developed a portal that allowed him to travel to alternate universes, and on one occasion, he did so. There he encountered life forms that were based on silicon, not carbon. There was a monster terrorizing the local population, and the scientist decided he'd somehow figure out how to save them, as he'd fallen in love with one of them.
Now, the scientist gets killed somehow, and it's up to the soldier to figure out the clues left behind by the scientist. The soldier eventually uncovers the portal, makes his way to the alternate universe, where his body reacts to the environment by activating all the unseen abilities given by the scientist.
Back then, the book I read had a picture of man's face, kind of looking skeletal.
If you have any clues, please let me know!
Thanks in advance,