Individualism is the idea that individuals can do more to help themselves than any government or group; that idea stands in opposition to collectivism. Individualism was popularised in the nineteenth century by the British philosopher John Stuart Mill and by his follower Auberon Herbert. Despite being the opposite of collectivism, however, some leftists also embrace individualism (albeit in a more anarchistic and nihilistic manner), such as Jean-Paul Sartre and the ACLU.
'Rugged individualism' is a term derived from 'individualism' and denotes the ideal of a righteous life in which the individual never finds that he needs help from anyone in order to remain both healthy and sane in a fallen world. In refusing the offer of the king of Sodom to take what many Bible commentators say was a rightful portion of the spoils of the war through which he rescued Lot, Abr(ah)am (Abraham) was motivated by a sense of rugged individualism in mind of God's promises to him.
Nonetheless, rugged individualism, while implicitly sought by all, is an ideal which is unattainable by mere fallen individuals (and thus by all nations made up of fallen individuals). Even Karl Marx, who founded the Communist dictatorial methodological paradigm of human improvement, was driven by the hope of creating a society in which individuals lived righteously without bureaucratic oversight. In contrast to Marx's dictatorially 'family'-centered methods toward that end was the narrowly immediate individualism advocated by Ayn Rand, in which civil society could be healthy only to the extent to which the individual's secular liberty, including his functional material capital, was in adverse relationship to the intelligent and humane extension of the dynamics of the natural family into the wider society. So, like defining human life as either anti-water or anti-salt, any paradigm which is in opposition either to the primacy of the individual as inherently free, or to the realities of the family as the core of a civil people, is destructive to the well-being both of individuals and of society.
The only person ever to have lived a life of rugged individualism is Jesus Christ, and he never preached individualism as such, but something of far more dense value: the spirit of the Mosaic Law, which has been God's standard to all nations since the second-youngest son of Jacob was prime minister (viceroy) in Egypt.