The T-shirt — the most humble, commonplace and yet iconic of garments — turns 100 this year.

Before there was the T-shirt there was the “union suit,” a one-piece undergarment with long sleeves. Great for colder climates; not so good where the temps hover at 100.

Resourceful individuals sheared the suit in two and hacked off the sleeves, leaving a cooler, round-necked, short-sleeved shirt that had enough tail to tuck in. The first iteration of the T-shirt was born.

Then the U.S. military came along and catapulted the T-shirt into history: In 1913 the U.S. Navy issued crewneck T-shirts for sailors to wear under their uniforms. Those first T-shirts were almost identical to what we wear today — crew-necked, short-sleeved and made of white cotton.

It didn’t take long for sailors and Marines in the Spanish-American War to toss their top layer, soiling their T-shirts but not their uniforms — and keeping cooler, too. It wasn’t until 35 years later that the Army realized the Navy had a good thing. The “quarter sleeve” shirt was issued by the U.S. Army in 1948.

Over the years, Hollywood’s influence has been both a curse and a blessing. In 1934’s “It Happened One Night,” the debonair Clark Gable took off his dress shirt, revealing his bare chest. T-shirt sales plummeted 75 percent. Following the release of “A Streetcar Named Desire” in 1951, when heartthrob Marlon Brando appeared on screen with his white T-shirt stretched tight across his manly chest, T-shirt sales skyrocketed.

Printed T-shirts began appearing in the 1940s, but the invention of Plastisol ink in 1959 opened the floodgates for screen-printed tees. Plastisol could stretch without cracking, was durable enough to survive multiple washings and didn’t irritate most skin types.

Starting in the early 1960s, tees became wearable art that celebrates everything from the likes of Andy Warhol’s iconic “Marilyn Monroe” to rock bands. They’ve been used to unify a movement or make fun of a politician; to promote charities, businesses and countless other causes both sacred and profane.

Along the way the unassuming tee sired a few variants. There’s the “deep-V,” a staple of the “Jersey Shore” crowd; the “polo” style with its collar and 3-button placket; and, of course, the tank — aka “wifebeater.” Most recently, manufacturers in the early 2000s stripped the shirts of their itchy labels, creating the tagless tee.

Today, businesses are built on the backs of tees. One local success story is Storyville, which opened in 2007 in an old house at the gates of LSU. The company now has four locations — one in Baton Rouge, two in New Orleans and one in Austin, Texas. Josh Harvey, who owns Storyville with his wife, Natalie, said the company turns out tees that reflect each community. Many of the designs come from local artists, and winners are selected by the Harveys and online polling.

“If you put New Orleans on a T-shirt and it’s half-way clever, it’s going to sell,” Harvey said. “If it’s Baton Rouge-centric, it doesn’t sell as well, but LSU T-shirts sell great. Austin is kind of in the middle.”

Regardless of what’s on the front, the eternal, essential T-shirt remains one of the least-changed designs in fashion history.

Not bad for a 100-year-old.