한철균 (韓鐵均), b. 1955-01-04
At the start of 2022 (and indeed currently as of February) he is the lowest rated professional on Go Ratings. At that time he was placed #900.
KBA Ko. Wiki Wikidata Go4Go GoR
Previous versions of this page have claimed that he became 6p in 1999 and 8p on 2012-04-16. These dates are unsourced and contradicted by the KBA website.