Very free thinking, but a GREAT author, nonetheless.

Some books by him:
Stranger in a strange place
The cat who walked through walls
I will fear no evil


I have a bunch others, given to be by my grandfather, and I've read those three. All are superb. I definitely recommend reading.

Stranger in a Strange Land


Great book...my favorite character is Jubal Harshaw and of course Heinlein based the character off of himself.
I've heard good things about all of his books, but SiaSL is the only one I've read so far.