J. W. (1)

The initials on the title page literally read I. W. but in the usage of the time this I is almost certainly meant to stand for what we would print as the letter J, and so this author's name is given as J. W. in reference works.

It's possible that the publisher meant to imply that John Webster (of The Duchess of Malfi fame) was the author of The Valiant Scot, but G. E. Bentley and Webster's various editors agree there is nothing in the play like Webster's work. So the initials are either a fraud, or someone else is meant.