Ad date unknown, but Spam was invented in 1937, and this ad calls it "new", so late 30s to early 40s is my guess.

Curiously, the product has an almost joke reputation in parts of the world, but in others it is considered a delicacy or luxury. Receiving a can of Spam from a mainland-US friend would be a gag gift, but it is given as a real gift in some places. That seems to be a historical result of huge amounts of Spam delivered into pacific islands by the US during WW-II. Soldiers would give the cans to the local food-stressed populations, and to this day it is associated with liberation and freedom. From there it was integrated into national cuisines. Countries like the Philippines have picked up the ball and run, inventing new local variations, incorporating local flavor and spice profiles, and using it in genuinely creative ways in traditional dishes.

Then came Python. To its credit, Hormel played along and leaned into the fun, rather than sending attack lawyers. They even created special Spam cans for Spamalot.

Spam.