Who is currently the longest serving head of a nation in March 2023?

As of March 2023, the longest serving current head of state is Hassanal Bolkiah, the current Sultan of Brunei, who came to the throne on 5 October 1967 following the abdication of his father, Omar Ali Saifuddien III. The longest serving head of state of a republic is Teodoro Obiang Nguema Mbasogo, who has been President of Equatorial Guinea since 12 October 1982. However, he assumed control of the country in a coup d'etat in 1979, serving as Chairman of the Revolutionary Military Council (which was renamed the Supreme Military Council) from August 1979 until his election as president in 1982.

https://en.wikipedia.org/wiki/List_of_current_state_leaders_by_date_of_assumption_of_office