The Paperback
In a great marketing ploy, there was a novelization to tie in with the film. There were a total of four versions, 2 in the UK and 2 in North America. The first two came out in the UK and US in 1979 and were called 'Gore Vidal's Caligula'. Once the lawsuits were all sorted out, a movie edition with pictures from the film came out in 1980 in each country. The copy on the far left is the first UK version, printed by Futura Press in 1979 and containing 208 pages. The middle book is the First US Printing from February 1979, by Warner Books (New York, NY).  This version of the book includes 16 pages of low quality black and white pictures from the movie; which wouldn't be released for another full year! This book consists of 222 pages, which may just be from a different type face. The copy on the far right is the official US movie version, probably from Feb 1980. The book was based on a little of all of the 7 variations of Gore Vidal's script, 1975 - 1976.

William Howard was the pseudonym for William Johnston (Born about 1935), the author responsible for scores of novels from the mid sixties right up to 1990 based on TV shows and screenplays. TV shows like 'Then came Bronson', 'Welcome back Kotter', 'The Brady Bunch', 'The Munsters', 'The Monkees', 'Happy Days', 'Get Smart' and 'Captain Nice.' His novels based on screenplays and scripts included 'Asylum', 'Klute', 'King', 'Caligula' and 'Dick Tracy'.

Caligula seems like it would be the only book he wrote that contains hard core sex. Johnston has the sex part down good. (Almost too good?) The book talks about Caligula's erection in the first paragraph! Because the book is based on the script, the dialogue is pretty well right from the movie, I can almost hear Malcolm and Teresa saying thier parts! Because of the movie, it doesn't seem that Howard is wasting much time on character development (also painfully missing from the movie), but it is neat to read parts that were cut from the movie and or script. As well, there are parts that were added to the movie. You can read more about the story in the Book Synopsis below.

You can tell that Gore really followed his Suetonius, who was the only historian to mention the story with Caligula's love of incest. The story of Antonia catching Caligula and Drusilla in the act is a good fictional account! Gore also screwed up the historial Roman names of characters, changed them to sound cooler? For example, they have Macro's full name as Naevius Sartorius Macro, and every Roman historian knows that it was Quintus Naevius Cordus Sutorius Macro!

One cool thing is that at least we get to hear what the characters were thinking, in the novel it is suggested that Macro really did not like Caligula, where in the movie we see him as nothing but devoted until he is double crossed.

I have to note the the Movie Novelization that is included with the
Imperial Edition Caligula DVD 2007 has almost no similiarity to the 1979 novel. The 74 page PDF file in the Imperial Edition is devoid of any sex, and follows the film version of the script closer than the 1979 novel. I have been told that the 1979 novel was the 1st Draft, and the version featured in the Imperial Edition DVD is the 3rd Draft by William 'Howard' Johnston.

Pictured below are two example of pure Suetonius, the one on the left was translated by Robert Graves (a bad combination), while the second seems to be the original, which it would seem that the "12 Caesars" was based on.
More about Suetonius
Complete Book Synopsis-HERE
Complete Movie Synopsis-HERE