When we agreed on the various masks for the Englishmen we decided that we wanted to try and keep them thematically grouped with images traditionally associated with the British (Jester, Knight, Dragon) but there were quite a few other aspects with Willmore's character that were easy to emphasize via mask. To that end we settled on making Willmore a pirate. This gets the fun connection to Willmore being the "rover" as well as the extremely debauched attitude Willmore displays throughout the show. Finally, Willmore makes quite a few nautical references (the best being "Would I could drop anchor in your cove") so it was just another affirmation of making Willmore into a pirate.
In planning out the design I spent a good deal of time in trying to figure out how best to communicate a pirate through a half mask. I looked into quite a few paintings/drawings of pirates, mostly of Blackbeard, though I also used a very well known modern example:
The first thought I had was that there was no way I could feasibly include a pirate hat in the design, and that actually giving Willmore a pirate hat wouldn't work out too well. So, next I was drawn to the bandanna, definitely something that could be accomplished in a half mask. Finally, I really wanted to give Willmore an eye patch. It's a visual that immediately helps define him as a pirate. The one problem with the eye patch was that The Rover is a show with lots of sword fighting, and putting an eye patch on someone wielding not one, but two swords is a safety fiasco waiting to happen. So I spent a good chunk of time figuring out a way to create the appearance of an eye patch on stage without actually obscuring Willmore's vision at all. In the end, I used two pieces of black lace sewn to the mask and it worked rather successfully. Here are some pictures of the sculpting process, as well as a final picture of the mask, on the actor with his costume: