- [Narrator] The steady supply of steak depended on the city's low-paid immigrants doing the dirty and dangerous work on the stockyards' killing floors.

- The throngs of German and Italian immigrants and Blacks from the South, all coming together and creating the industrialization of the American food supply.

- [Narrator] While slaughterhouse workers couldn't afford regular steak dinners, many could afford to take home cheaper, sinewy scraps of beef.

And using a bit of creativity and just the right amount of spice, Italian immigrants on the Near West Side turned that tough meat into a tender, juicy sandwich.

Word is that slicing the meat thin made it easy to frugally feed a lot of people at Depression-era weddings.

The move from wedding dish to beloved street food happened in the late 1930s with the opening of Al's #1 Beef.

- As Chris Pacelli, who runs Al's #1 Beef, tells it, his uncle, Al Ferrari, he had just got outta jail and his friend said, "Hey, how about if we open a bookie joint together?"

And he said, "Okay, and I'll have the front where I'll sell beef sandwiches."

Apparently he was, he sold so many that he said, "I'm gonna break off from this bookie joint.

I'm gonna start a legit business."

(gentle music) - My dad grew up with these guys, alright, with Chris, Bishop Bonsey from Al's Beef.

My dad grew up across the street.

They swear by this that they're the inventors.

- You know, everybody's got their own way of doing it.

You know who makes it this way?

Who makes it that way?

But this is the original way that it's started.

- Then you have other factions swearing that they're the inventor.

And I've done a lot of digging and it's, I mean, people, people will cut you.

- [Michael] Italian beef is so simple.

I'm not sure that there is such a thing as someone who invented Italian beef.

- [Chris] We start off with the pop round.

- [Paul] It's a cheap cut of meat.

You can use eye of round, you can use chuck.

- Rubbing it, making it flavorful, roasting it low and slow.

- After three and a half hours, we'll pull this out.

But all the natural juices drip.

- All in the efforts of making it succulent.

And then you're slicing it very, very thing.

- And you can see right through it almost.

- Want a dip?

- [Customer] Yeah.

- [Paul] Soaking in its juices and putting it on an Italian roll, and it's got to be an Italian roll.

If you try to put that on French bread or on a hot dog bun, it's gonna dissolve in your hands.

- [Jeff] Then you top it with sweet peppers and/or hot peppers, and you eat it standing up.

It's juicy, it's crunchy, it's unctuous, it's oily, it's beefy, it makes you sweat.

- [Chris] Because it's so juicy, you gotta lean back, put your forearms on the counter so you don't get it all over you.

- [Narrator] The sloppy sandwich remained a local secret until a hit TV show, "The Bear," introduced Italian beef to the world.

- Margo, here you, my love.

That's for you young lady.

- [Tina] What's this?

- That's Italian beef sandwich.

- What's an Italian beef?

- You know what a French dip is?

- Yeah.

- That's an Italian dip.

- [Tina] Okay.

- I hope you, I hope you like it.

I'm Richie.

- I'm Tina.

Thank you, Richie.

- Nice to meet you.

- [Narrator] They also popularized the spicy oily condiment that topped it all off, giardiniera.

- You're not gonna find these preserved, brined vegetables in olive oil really anywhere else except for Chicago.

- Carmy did have my giardiniera in his fridge, Season 2 Episode 2.

He opens the fridge after a long night at The Bear, and there it is.

It was the rear label, but the giardiniera was there.

I don't think he opened it though.

That would've been nice.