Some of what Michel Foucault says about ethics and moral theory seems close to what the British philosopher Bernard Williams says. Williams read Foucault but does not say much about him. I would say that Willams’ criticisms of moral theory flow out of his work on ethics from the late 50s until his death in 2003, which was rooted in Anglosphere academic tradition in philosophy (Conceptual-Analytic), including a critical discussion of Utilitarianism. An increasing awareness of Continental European style philosophy (Historical-Interpretative) had an influence on him, but probably confirmed and modified his emergent views rather than bringing them about.
In books like Ethics and the Limits of Philosophy, Williams criticises the view that ethical philosophy should be primarily concerned with moral theory, theories of the right and the good, of their meaning and their applications. He argued instead that moral/ethical philosophy is defined institutionally rather than through pure analysis, that is it has a history in which there is an evolving set of norms about what morality is and where it’s philosophical discussion can be found. A similar discussion aesthetics can be found in Arthur Danto’s writings, who lie Williams was an ‘Analytic-Conceptual’ philosopher with some ‘Historical-Intepretative’ interests.
Williams prefers talk about ethics as a concrete field in which we are concerned with ethical situations and behaviour rather than pure definitions in moral theory. This parallels Foucault’s concerns with ‘ethos’, a Greek word equivalent to ‘mores’ in Latin, and related to the idea of ‘custom’ in English. For Foucault, ethos is distinct from concerns with natural reality, referring to the possibilities of aesthetics, style, and care of the self, for the individual. That could sound individualistic to the extreme, but on Foucault’s understanding includes the need for reciprocity and respect for others’ individuality if there is to be a really successful ethos.
In distinction from Williams, Foucault is less concerned with exact boundaries and illustrative thought experiments. Though Williams pushed at the limits of the conceptual-analytic mode in philosophy, he always revolves around it in his work. Concern with exact limits and hypothetical definition challenging is not so much in Foucault’s mode, though he was certainly concerned with the experience of limits of various kinds. The difference between a concern with subjective experience and a concern with experiments in philosophically charged hypothetical situations is a distinction between the two philosophical approaches.
Hegel also favoured a distinction between morality and ethics to the advantage of ethics. Though in morality he was just as much concerned with moral imagination and experience as with theory. Hegel saw morality as based on subjectivity in thought and experience, so self-referring and collapsing into a concern with the purity of that individual and the superiority of that individual, rather than the life of the ethical community. Foucault differs from this in that he sees an ethical community as much more fragmented and divided by different ways of living for which Hegel can allow; Williams differs from this in his concern with the role of luck and external influences in ethics, which Hegel always tries to resolve through some display of inner necessity.