The copyright symbol © was created by the authors of section 18 of the U.S. Copyright Act of 1909 which states, "...the notice may consist of the letter C inclosed within a circle, thus: ©, accompanied by the initials, monogram, mark, or symbol of the proprietor..."

Since the symbol is a work of one or more government employees as part of their duties under U.S. law the © symbol is public domain so nobody has ever legally owned or can ever legally claim exclusive ownership of the symbol.

Sources:

https://www.copyright.gov/history/1909act.pdf

https://www.usa.gov/government-works