Heinlein is one of the Big Three of science fiction writers. Along with Isaac Asimov and Arthur C. Clarke, our guy brought science fiction into its golden age. Their stories showed that science fiction was much more than alien invasions, ray guns, and bikini-clad damsels-in-distress. In fact, it could be—gasp!—serious literature.
Heinlein originally published Stranger in 1961 but was required to heavily edit the manuscript by about 60,000 words. After his death, his widow published the unedited version of Stranger. Now opinion is divided over which version is better. As a result, both versions of the novel are still published today, fifty years after the original's publication date. Which one do you prefer? (Source.)
The waterbed used to contain Smith in the opening chapters may seem boring by today's standards, but in 1961, it was totally sci-fi. In fact, Heinlein's concept of the waterbed predates commercial waterbeds in the U.S. by about seven years. When Charles Hall tried to patent waterbeds in 1968, the patent office denied him. Their reason? They claimed waterbeds' existence in prior art, and by prior art, they meant this book. (In fact, other cultures did have waterbeds before Heinlein wrote about them.) (Source.)
Heinlein coined the term grok specifically for this novel. The word slowly filtered into our cultural lingo as the novel became a cult classic in the 60s. Today both the Oxford English Dictionary and the Merriam-Webster Dictionary contain entries for grok. The word has also appeared numerous times in pop culture. For example, Futurama's Number 9 Man uses the word, and you can buy buttons and shirts saying "I grok Spock" at Trekkie conventions everywhere. The word even has its own Wikipedia page, so you know it's legit.
Oberon Zell-Ravenheart was so enamored with Stranger's Church of All Worlds that he started his own church, blending neopaganism with ideas from Mike's religion. He called it the Church of All Worlds (points deducted for lack of originality). The church's official magazine is titled "Green Egg," a title partly inspired by Mike's catchphrase, "I am only an egg." Heinlein had nothing to do with the founding or running of the church, but he was definitely the inspiration. (Source.)
The title of Jubal's story "A Martian Named Smith" (38.98) was one of the working titles for Stranger in a Strange Land. We're glad he went with Title 2.0.