Lasse Mårtenson had tried to represent Finland already in 1963, when his Kaikessa soi blues (written by Toivo Kärki & Reino Helismaa, the most popular and productive song writing team in Finnish pop music history) narrowly lost the bid to Laila Halme's Muistojeni laulu. In 1964 he was already an established and experienced songwriter and singer and his own composition Laiskotellen (words by Sauvo Puhtila) faced no real challenge in the Finnish selection, on his second attempt Lasse Mårtenson was chosen to represent Finland in the Eurovision Song Contest held in Copenhagen.
There's no existing video recording of the 1964 Eurovision Song Contest, but the soundtrack suggests that he was well at ease on Copenhagen stage, even though he got mixed up with the lyrics at one point. Laiskotellen has never been a particular favourite of mine, but one cannot be but proud of his relaxed and professional performance. According to the result, 7th place among 16 participants, the juries agreed. Laiskotellen became one of Lasse's favourite songs and he recorded the song in addition to the finnish version at least in his maternal language swedish and italian (Cara Domenica). You can watch a television performance of the swdedish version and a snippet of a 1992 performance of the finnish version on YLE's Open Archive.
At the time of his Eurovision participation Lasse Mårtenson was married to his Swedish Eurovision collegue Siw Malmkvist, who had represented her home country in 1960 before their marriage and would take part again in 1969 for Germany when she and Mårtenson were already divorced. Tove Mårtenson is probably the only person in the world who can claim to have parents having represented three different countries in Eurovision in three different languages.
Already a year after his Eurovision participation Mårtenson wrote and sang a song with Marjatta Leppänen in scandalous 1965 Finnish selection. Their song Iltaisin won the public vote but this was overruled by the so called Nordic jury, which chose Aurinko laskee länteen instead (sung by Viktor Klimenko and written by the same team that had penned Lasse's entry 1963). In 1967 in Vienna he took part as a composer of the song Varjoon suojaan, and he would continue to take part in the finnish selection as both composer (1966, 1967, 1971, 1973, 1975 and 1977), artist (1966, 1967, 1971, 1973 and 1977) and host (1987, you can watch the 1980's Finnish selections Yle's Living Archive).
Pop music was not the only field Mårtenson used his talent. He performed and recorded jazz and blues, and in 1967 he topped the Finnish album charts with a gospel album Voisiko sen sanoa toisinkin. In the late 1960's he started acting and composed music for movies and films, most famously for a tv drama Stormskärs Maija (or Myrskyluodon Maija in finnish). The exquisite theme of the series became his most loved and most performed song, which Anna Järvinen chose as her walk in music in Melodifestivalen 2013.
Lasse Mårtenson was a multitalented and loved musician right until his death at the age of 81 in 14. May 2016. The only sour note came in 2006, when a group of young musicians made a tribute album and concert on his honour. Surprisingly Mårtenson disapproved and loudly voiced his dissatisfaction of the new versions of his work.
My points 3/5.