Magnus Haakonsson (Old Norse: Magnús Hákonarson, Norwegian: Magnus Håkonsson; 1 May 1238 – 9 May 1280) was King of Norway (as Magnus VI) from 1263 to 1280 (junior king from 1257). One of his greatest achievements was his modernisation and nationalisation of the Norwegian law-code, after which he is known as Magnus the Law-mender (Old Norse: Magnús lagabœtir, Norwegian: Magnus Lagabøte). He was the first Norwegian monarch known to personally have used an ordinal number, although originally counting himself as "IV".