The former chief executive of Landsbanki of Iceland was sentenced to prison on Wednesday, the third of the top executives of the country's three largest banks that the government has successfully prosecuted and jailed for misconduct during the financial crisis. Iceland was one of the countries hardest hit by the financial crisis and was forced to nationalize its three largest lenders in 2008. Mr. Arnason is the third former chief executive of an Icelandic bank to be ordered jailed for misdeeds in the run-up to the nationalization of Landsbanki and two other of the island nation's biggest lenders. Kaputhing, at one time Iceland's largest lender, saw its chief executive, Hreidar Mar Sigurdsson, and its chairman, Sigurdur Einarsson, convicted of market manipulation last year. Mr. Sigurdsson was sentenced to five and a half years in prison, while Mr. Einarsson was sentenced to five years in prison. Larus Welding, the former chief executive of Glitnir, the first of the banks to be nationalized, was convicted of fraud in 2012. The Icelandic lenders expanded beyond their borders during the boom years, only to collapse under a mountain of debt as financial conditions worsened in 2008. After the banks were nationalized, Iceland's government restructured them, purging their management and refusing to bail out foreign bondholders who held tens of billions of dollars of the banks' debt. A special prosecutor, Olafur Hauksson, was appointed to investigate the actions of bank executives in the run-up to the financial crisis.