Dr. Pentti Ilkka Olavi Arajärvi (born 2 June 1948, Helsinki) is a Finnish Doctor of Law, Professor Emeritus and Docent of the University of Helsinki,^[1][2] a former civil service official and a Social Democratic politician from Helsinki.^[3] Arajärvi was awarded the honorary title of valiokuntaneuvos ("Committee Counselor") for his work in parliamentary committees. He is the spouse of Tarja Halonen, who was the President of Finland between 2000 and 2012.

Arajärvi was elected to the Helsinki City Council in the 2012 municipal elections.

On 26 August 2000, after a relationship of more than fifteen years, Arajärvi married his longtime partner, Tarja Halonen, who was at the time the President of Finland, in a civil ceremony at her official residence, Mäntyniemi. The couple has no children. Arajärvi has an adult son from a previous relationship.^{[citation needed]}