Author of safe Tcl, a system for secure execution of scripts, later folded into the Tcl core as part of the work on interpreter hierarchies (slave interpreters, see interp).
Marshall's done much else besides. He wrote early SNMP- and MIME-handling software in Tcl.
See also his BOOK How to Manage Your Network Using SNMP.
Conversely, Marshall realizes that sometimes a small white lie can help avoid pain and as a friend, he has no trouble serving as a subject of that white lie. It's thinking like this that made Marshall the success he is today.