What the the default sans serif font in LaTeX? If it is a clone what is it based upon?
The default sans serif font used by LaTeX is Computer Modern Sans Serif, a font designed by Knuth as part of the Computer Modern (meta)family.
The Roman variant is inspired to Monotype Modern 8A; the Sans Serif variant has been generated by a "meta" process, without any previous model in mind, I believe.
When the output encoding is T1 (
European Modern fonts have been converted to Type1 outline fonts as part of the CM-Super project. Another very similar font family is Latin Modern, also available in Type1 format (
When XeLaTeX or LuaLaTeX are used, the default is not changed, so one gets Computer Modern (Roman and Sans Serif). However, a call of
will change the default fonts to Latin Modern, as these are also available on all recent TeX distributions as OpenType fonts. There is, actually, an OpenType version of Computer Modern (CMU fonts), also in the TeX distributions.