David Clarke is no longer Milwaukee County's sheriff.
Clarke gave no reason for his resignation in a one-paragraph letter to the county clerk that was obtained by NBC News.
Gov. Scott Walker issued this statement, saying he will "move forward with the process of filling the vacancy as soon as we are formally notified of the resignation by Milwaukee County".
Clarke has risen to national prominence in recent years, largely due to his appearances on conservative media programs and provocative social media posts.
It remains unclear what Clarke will do next.
A frequent Fox News contributor, Clarke has been a staunch supporter of President Trump's tough-on-crime and tough-on-immigration positions.
Some Wisconsin conservatives had encouraged Clarke to challenge U.S. Sen.
In June of this year, Clarke reportedly withdrew his name from consideration for a role in the Department of Homeland Security. Tammy Baldwin, a Democrat, but he repeatedly rejected their overtures.
The sheriff could not immediately be reached for comment.
Clarke recently published a memoir, "Cop Under Fire".
He was later accused of plagiarism in his master's thesis at the Naval Postgraduate School. But as Nick Wing explained at HuffPost, the number of deaths is highly unusual: "Based on an analysis of The Huffington Post's jail death database, other jails that have four deaths in a year are several times the size of Clarke's downtown jail site, which has a capacity of 960".