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The existence and properties of the sigma meson have been controversial foralmost six decades, despite playing a central role in the spontaneous chiralsymmetry of QCD or in the nucleon-nucleon attraction. This controversy has alsobeen fed by the strong indications that it is not an ordinary quark-antiquarkmeson. Here we review both the recent and old experimental data and the modelindependent dispersive formalisms which have provided precise determinations ofits mass and width, finally settling the controversy and leading to its newname: $f_0(500)$. We then provide a rather conservative average of the mostrecent and advanced dispersive determinations of its pole position$\sqrt{s_\sigma}=449^{+22}_{-16}-i(275\pm12)$.  In addition, after comprehensive introductions, we will review within themodern perspective of effective theories and dispersion theory, its relation tochiral symmetry, unitarization techniques, its quark mass dependence, popularmodels, as well as the recent strong evidence, obtained from the QCD $1/N_c$expansion or Regge theory, for its non ordinary nature in terms of quarks andgluons.

From controversy to precision on the sigma meson: a review on the status of the non-ordinary $f_0(500)$ resonance