While working on the screenplay for Batman (1989), he was invited by comic
book editor Denny O'Neil to write the Batman comic. It was during this time
that he created (with Denys Cowan) the character of Ducard that went on to
feature prominently in Batman Begins (2005).
In 1989, Sam Hamm wrote a script for a proposed movie version of the 1985 graphic novel Watchmen. The script was never used, and a movie was made a full two decades later in 2009. The full script is easily found with a web search as of now (2017).