I found this interesting:
Michigan does not have a live mascot comparable to Ohio's Brutus Buckeye. The Athletic Department has steadfastly maintained that such a symbol is unnecessary and undignified and would not properly reflect the spirit and values of Michigan athletics. Over the years a number of individuals and groups have proposed mascots in a variety of wolverine costumes but the department has refused to sanction them. Instead, it continues to rely on the wolverine itself as the symbol of Michigan sports.
As early as 1861, the students and alumni began referring to themselves as "Wolverines." How the ferocious animal came be associated with the state and adopted as the university mascot remains a bit of a mystery, but there several theories.
The simplest reason for the wolverine nickname would be that the animal was abundant in Michigan at some time. However, all the evidence points otherwise, as there has never been a verified trapping of a wolverine inside the state's borders, nor have the skeletal remains of a wolverine been found within the state's 96,705 square miles.
The great Michigan football coach Fielding H. Yost had a theory for the nickname, which he wrote about in the Michigan Quarterly Review in 1944. Yost felt that the reason for the nickname concerned the trading of wolverine pelts which occurred at Sault Ste. Marie for many years. The trading station served as an exchange between the Indians, other trappers and fur traders, who would eventually ship the products off to the Eastern United States. Because many of the furs were in fact wolverine pelts, the traders may have referred to them as "Michigan wolverines," leading to the state nickname and ultimately to the University of Michigan symbol.
Eight years later, in the Michigan Quarterly Review of 1952, Albert H. Marckwardt presented another theory for the "wolverine" name. Marckwardt's reasoning is based the fact the Michigan was first settled by the French in the late 1700s. The appetites of the French were judged to be gluttonous or "wolverine-like" and therefore, the nickname wolverines was conferred upon them.
The last theory derives from the border dispute between Michigan and Ohio in 1803, often referred to as the "Toledo War." While the two sides argued over the proper setting of the state line, Michiganders were called wolverines. It is unclear, however, whether the Michigan natives pinned this name upon themselves to show their tenacity and strength, or whether Ohioans chose the name in reference to the gluttonous, aggressive, habits of the wolverine. From then on, Michigan was labeled the "Wolverine state" and when the University of Michigan was founded, it simply adopted the nickname of the state it represented.
Fielding Yost set out to find a wolverine in 1923, after seeing Wisconsin carry live badgers along with its football team. Yost's desire met with difficulty, as the coach had problems finding a dealer of live wolverines. After a letter to 68 trappers yielded no mascot for his team, Yost expanded his wish to any wolverine, alive or dead.
Yost was finally able to obtain a mounted wolverine from the Hudson's Bay Fur Company in the fall of 1924, but his quest for a live one continued. In 1927, 10 wolverines were obtained from Alaska and placed in the Detroit Zoo. On big football days, two of these wolverines were brought into Michigan Stadium and carried around in cages.
Bennie and Biff on display at the dedication of Michigan Stadium, 1927
However, the animals grew larger and more ferocious, and as Yost states, "It was obvious that the Michigan mascots had designs on the Michigan men toting them, and those designs were by no means friendly." Therefore, the practice of bringing wolverines into the stadium had to be discontinued after only one year. However, one of the wolverines was not returned to the Detroit Zoo. Instead, "Biff" was put in a cage at the University of Michigan Zoo where students were able to visit him at all times. In 1937, the Chevrolet Motor Company donated a wolverine (as well as the cage to keep it in) to the University of Michigan. A contest was held to name the new mascot and "Intrepidus" was the winning entry. It is unclear how long Intrepidus survived, but it is known that no live wolverines have been in Michigan Stadium in the last half-century.