* The "Tiger" mascot of Princeton University: While its exact origins are debated, evidence suggests the tiger mascot dates back to the late 1800s, making it one of the oldest in existence.
* The "Fighting Illini" mascot of the University of Illinois: While their mascot has evolved over time, the "Chief Illiniwek" figure, representing an indigenous warrior, was used from 1926 until its retirement in 2007 due to cultural sensitivity concerns.
* The "Golden Bear" mascot of the University of California, Berkeley: Their mascot dates back to the early 1900s, and the current iteration, Oski, is one of the most iconic and recognizable mascots in college athletics.
It's worth noting that mascot usage wasn't formalized or widespread until the early 20th century. Early "mascots" might have been just a single animal, chosen by a team, rather than a specific costumed figure.
Therefore, while these examples are strong contenders for "first," the exact origin of the concept is still debated and likely lost to history.