Peter Langkjær Madsen (Danish: [ˈpʰe̝ˀtɐ ˈlɑŋˌkʰeˀɐ̯ ˈmæsn̩]; born 12 January 1971) is a Danish convicted murderer and former entrepreneur. In April 2018, he was convicted of the August 2017 murder of Swedish journalist Kim Wall on board his submarine, UC3 Nautilus, and sentenced to life imprisonment.