(written from a Production point of view)
Masterson "Mast" Alexander is the actor who portrayed the Kriosian guard in the Star Trek: Enterprise episode "Precious Cargo". He received no credit for his appearance and was identified by the name tag of his costume which was sold off on the It's A Wrap! sale and auction on eBay. 
He studied acting at the Actors Movement Studio and the William Esper Studio, both located in New York. Beside stage plays such as Bram Stokers Dracula and Julius Caesar he appeared in several commercials and television series including The Larry Sanders Show, Lookwell, Equal Justice, and All My Children. He played the leading roles in the independent films Barely Surviving and The FX Files and was featured in Woody Allen's comedy Sweet and Lowdown (1999, with Brian Markinson) and in the short comedy Little Sister (2000).