I don't know where this preception of Steinbrunner being the richest owner has come from but it's simply incorrect. Before his death, Steinbrunner was worth an approximate $1.3 Billion according to Forbes. Wealthy, but no where near some other owners.
Currently the richest single owner in North American professional sports is Paul Allen (Net Worth: $13.5 Billion) who owns the Portland Trailblazers (NBA) and Seattle Seahawks (NFL).
The richest prospective owner (meaning someone who has shown interest of acquiring an professional sports property but has not been able to secure a deal for one yet) that I know of is David Tompson (Net Worth: $19 billion) who is working towards getting an NHL team for the Canadian city of Winnipeg, Manitoba.
The richest owner outright is the Ontario Teachers Pension Plan who own 66% of Maple Leaf Sports and Entertainment which in turn owns the Toronto Maple Leafs (NHL), Toronto Raptors (NBA), and Toronto FC (MLS) along with the minor league club the Toronto Marlies (AHL). The OTPP' estimated assets exceeds $96.4 Billion.
Paul Allen
Paul Allen - Seattle Seahawks
Paul Allen owner of Seattle Seahawks cofounder of Microsoft
Dallas Cowboys
Dallas Cowboys
It is the owner of Ranbaxy
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The actor Will Smith is not an owner or minority owner of an NFL Franchise. While he is not an NFL owner, Will Smith is a minority owner of the NBA's Philadelphia 76ers.
Peyton Manning
the owner of beer chang
Mike Brown - NFL owner - was born in 1937.
The Seahawks. (Paul Allen is the reason)