"Victor Appleton" is a pseudonym used by the Stratemeyer Syndicate associated with the Tom Swift series of books. Writers of these books included Howard Roger Garis, John W. Duffield, W. Bert Foster, Debra Doyle with James D. Macdonald, F. Gwynplaine MacIntyre, Robert E. Vardeman, and Thomas M. Mitchell.
"Victor Appleton" was used for the original Tom Swift series (1910-1941). "Victor Appleton II" was used for the later Tom Swift Jr. series (1954-1971), with different actual authors than the original series. "Victor Appleton", without any suffix, was revived for a third (1981-1984) and fourth (1991-1992) series of Tom Swift books.
The fourth and fifth series of Tom Swift books were owned by Simon and Schuster publishers.
There are also two fan-generated tribute series unofficially "available" under the pseudonym Victor Appleton. (6 and 7 here)
Victor Appleton was also used by the Stratemeyer Syndicate for the Don Sturdy series, the Moving Picture Boys and the Movie Picture Boys.
Please do not combine the 7 Victor Appletons or combine any of the pseudonyms with ghostwriters who wrote under this name.
WHY ARE THERE 7 VICTOR APPLETONS?
To sum up, The first three were owned by the Stratemeyer Syndicate (Victor Appleton, Victor Appleton II, and Victor Appleton) and the 4th and 5th are owned by the publisher Simon and Schuster. 6 and 7 are fan writers who are not officially using the name Victor Appleton II. Each set of V.A.s are different people writing under different time periods and regimes. By keeping them separated you are honoring the history and authorship of the 7 different series that exist for Tom Swift--5 official series and 2 fan series.