The first-season Star Trek episode "What Are Little Girls Made Of?" has a few memorable things that stand out. It gives us our second evil duplicate Kirk of the series, we get some backstory for Majel Barrett's nurse Chapel... but arguably what sticks in the minds of fans the most is Ted Cassidy as ominous android Ruk.

At this time, Ted Cassidy was fresh off the ending of The Addams Family where he enjoyed a regular role as Lurch, the family butler. In his book Star Trek Memories, William Shatner talks about how Cassidy was cast as the seven-foot-tall, menacing android. Prior to filming, Star Trek's makeup artist, Freddie Phillips asked Cassidy to come in for a makeup test.

"Cassidy sat down in Phillips' undersized makeup chair and allowed the artist to transform him from a smiling young actor to an evil, hulking monster," Shatner writes. "First Freddie covered Ted's head with a latex skinhead wig; then he applied a sort of greyish-green base coat over Cassidy's entire face. Once all that was done, Phillips darkened the area around each of the actor's eyes and employed a black grease pencil to sharpen the angles of Ted's cheekbones, forehead and chin. The end result was quite frightening and really served to drain all the humanity from Cassidy's face."

They got him decked out in a potential costume, then sent him over to Gene Roddenberry's office for approval on the look. (Roddenberry, Trekkies will know, was the creator and executive producer of Star Trek.)

Roddenberry was delighted by the looming android, but asked Cassidy to help him out with a prank before he became human once more. A particularily annoying salesman had been badgering Star Trek cast and crew alike for awhile, trying to get anyone who would listen to buy a suit from him. He'd finally worn down Roddenberry into meeting with him — and he was on his way to meet with him now.

"Flash forward half a minute," Shatner explains, "and you'll find that Gene, [Trek costume designer] Bill Theiss, Freddie, [associate producer] Bob Justman and I are all huddled outside the side door of Gene's office, giggling... with his feet up on Gene's desk and Gene's phone at his ear, sat this seven-foot-tall bald green creature that Bill and Freddie has created, and that Ted Cassidy was now bringing to life wonderfully, pretending that he was Roddenberry."

Shatner says that Cassidy took to the role with enthusiasm, "yammering machine-gun style into the phone and saying things like 'Babe, we need thirty K added to the special effects budget or the Enterprise ain't gonna fly.'"

At this point the persistent salesman knocked on the door, and Dorothy Fantana (then Roddenberry's secretary, later known by her pen name of D.C. Fontana as one of the most beloved Trek writers of the series) let him in. "The doorknob turns, the door opens up and this suit-hawking salesman's come face-to-face with a monster. Cassidy now raises one finger at the guy and continues talking into the phone, milking this performance with everything he's got."

Instead of bolting out the door as Roddenberry expected, the salesman turned the tables... and proceeded to pitch a "big and tall" sale to this green-tinted android. 

"Upon hearing that, Gene, Freddie, Bill, Bob and I explode in laughter... loudly yukking it up as we come stumbling, teary-eyed into the room. The salesguy immediately figures out the joke, but instead of being embarassed or angry, he remarkably, and without a moment's hesitation, starts trying to sell cheap suits to all six of us."

The joke wasn't entirely on the salesman, however — Shatner adds that "guilt-ridden over the prank, Gene and I each bought some really ugly plaid pants."