Frank Vlastnik (born May 30, 1969)^[1] is an American author and actor known for his roles in several Broadway productions.

Vlastnik was born in Peru, Illinois. He graduated from Illinois Wesleyan University in 1987.^[2]

Vlastnik is best known as an original cast member in the short-lived musicals Big, Sweet Smell of Success, and A Year with Frog and Toad on Broadway, and Off-Broadway in Stephen Sondheim's musical Saturday Night.^[3] His big break came when he was cast as the original understudy for the leading role in Big. He later starred on and off-Broadway in A Year with Frog and Toad in which he played the 'Snail with the Mail', and was featured on the cast album. He also guest-starred on episodes of Law & Order, The Good Wife, Boardwalk Empire, Person of Interest, and Elementary. He is the co-author of the books Broadway Musicals and Sitcoms, both published by Black Dog & Leventhal Publishers.^[4][5]

In 2021, Vlastnik co-authored The Art of Bob Mackie, about the life and career of Bob Mackie.^[6]