Icelandic educator and politician who became president of Iceland in 1996. He is known for his strong advocacy of environmental issues.

Grímsson was born in a small fishing town on Iceland's northwestern peninsula. He graduated from the Reykjavík Lyceum in 1962 and then studied in England, where he received a B.A. (1965) and a Ph.D. (1970) in political science from the University of Manchester. He returned home to become a lecturer in political science at the University of Iceland and was appointed professor in 1973.

In the early 1970s Grímsson became well known as a moderator of television talk shows, often engaging in discussions on controversial political and social subjects that generated heated debate. He joined the leftist People's Alliance Party and served as party chairman from 1987 until 1995, when he resigned to run for president. Grímsson was first elected to the Althingi (parliament) in 1978 and served off and on until 1995, including one stint (1988–91) as minister of finance. As president (1984–90) of the Parliamentarians for Global Action, he traveled widely to persuade political leaders of major countries to strengthen the cause of world peace, for which he received the Indira Gandhi Peace Award.

During his political career, Grímsson tended to lean to the left in his views and developed a reputation for being a vigorous debater on the political scene. Despite widespread reservations about naming a career left-wing politician to the primarily ceremonial office of president, he was elected to the post in 1996 for a four-year term and was reelected in 2000 and 2004. As president, Grímsson was expected to stay above the fray of domestic politics, and he mostly followed precedent—except in 2004, when he vetoed legislation that had been passed by the parliament, the only time this had happened since the Republic of Iceland was established in 1944. The legislation, which had to do with limits on ownership of television stations, was subsequently rescinded.

As global warming and escalating fossil fuel costs were high on the international agenda, Grímsson was actively involved in promoting solutions. During his term of office, Iceland—with a population of only 310,000—had become a leading centre for research into and development of alternative energy, especially geothermal (geothermal energy). Grímsson drew attention in 2007 when he endorsed an ambitious new research project outside Reykjavík, where an international team of scientists planned to reduce carbon dioxide emissions by sequestering CO₂ in rock deep beneath the ground. He remained president for a fourth term beginning in 2008 after elections were cancelled because no one had stepped forward to run against him.