With biblatex there are two solutions.
The easy solution prints the full name the first time any work is cited.
\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[style=authoryear, backend=biber, citetracker=true]{biblatex}
\addbibresource{biblatex-examples.bib}
\DeclareNameFormat{labelname}{%
\ifciteseen
{\ifcase\value{uniquename}%
\usebibmacro{name:family}
{\namepartfamily}
{\namepartgiven}
{\namepartprefix}
{\namepartsuffix}%
\or
\ifuseprefix
{\usebibmacro{name:given-family}
{\namepartfamily}
{\namepartgiveni}
{\namepartprefix}
{\namepartsuffixi}}
{\usebibmacro{name:given-family}
{\namepartfamily}
{\namepartgiveni}
{\namepartprefixi}
{\namepartsuffixi}}%
\or
\usebibmacro{name:given-family}
{\namepartfamily}
{\namepartgiven}
{\namepartprefix}
{\namepartsuffix}%
\fi}
{\usebibmacro{name:given-family}
{\namepartfamily}
{\namepartgiven}
{\namepartprefix}
{\namepartsuffix}}
\usebibmacro{name:andothers}}
\begin{document}
\cite{sigfridsson}
\cite{knuth:ct:a}
\cite{sigfridsson}
\cite{knuth:ct:b}
\cite{vizedom:related}
\cite{knuth:ct:a}
\cite{vizedom:related}
\cite{knuth:ct:b}
\printbibliography
\end{document}
The second solution prints each name in full only the first time it appears. This is more complicated since names need to be tracked and not the entries. The code implements a new option nametracker. If set to context names will be tracked separately for the text and footnotes, if set to global (alias true) names will not be tracked separately. nametracker=off disables name tracking. This idea is based on Citing author's full name in biblatex the first time it appears, Automatically cite author's name in full the first time it appears and https://github.com/LukasCBossert/biblatex-archaeologie/pull/124
\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[style=authoryear, backend=biber]{biblatex}
\addbibresource{biblatex-examples.bib}
\makeatletter
\newrobustcmd*{\cbx@nametracker@global}[1]{%
\xifinlistcs{#1}{cbx@bseen@names@\the\c@refsection}
{}
{\listcsxadd{cbx@bseen@names@\the\c@refsection}{#1}}}
\newrobustcmd*{\cbx@nametracker@context}[1]{%
\iftoggle{blx@footnote}
{\xifinlistcs{#1}{cbx@fseen@names@\the\c@refsection}
{}
{\listcsxadd{cbx@fseen@names@\the\c@refsection}{#1}}}
{\xifinlistcs{#1}{cbx@bseen@names@\the\c@refsection}
{}
{\listcsxadd{cbx@bseen@names@\the\c@refsection}{#1}}}}
\newrobustcmd*{\cbx@ifnameseen@global}[1]{%
\xifinlistcs{#1}{cbx@bseen@names@\the\c@refsection}}
\newrobustcmd*{\cbx@ifnameseen@context}[1]{%
\iftoggle{blx@footnote}%
{\xifinlistcs{#1}{cbx@fseen@names@\the\c@refsection}}%
{\xifinlistcs{#1}{cbx@bseen@names@\the\c@refsection}}}
\DeclareBibliographyOption[string]{nametracker}[true]{%
\ifcsdef{blx@opt@nametracker@#1}
{\csuse{blx@opt@nametracker@#1}}
{\blx@err@invopt{nametracker=#1}{}}}
\def\blx@opt@nametracker@global{%
\let\cbx@ifnameseen\cbx@ifnameseen@global
\let\cbx@nametracker\cbx@nametracker@global}
\let\blx@opt@nametracker@true\blx@opt@nametracker@global
\def\blx@opt@nametracker@false{%
\protected\long\def\cbx@ifnameseen##1##2##3{##3}%
\let\cbx@nametracker\relax}
\def\blx@opt@nametracker@context{%
\let\cbx@ifnameseen\cbx@ifnameseen@context
\let\cbx@nametracker\cbx@nametracker@context}
\appto\blx@secinit{%
\ifcsundef{cbx@bseen@names@\the\c@refsection}
{\global\cslet{cbx@bseen@names@\the\c@refsection}\@empty}
{}%
\ifcsundef{cbx@fseen@names@\the\c@refsection}
{\global\cslet{cbx@fseen@names@\the\c@refsection}\@empty}
{}}
\InitializeCitationStyle{%
\global\cslet{cbx@bseen@names@\the\c@refsection}\@empty
\global\cslet{cbx@fseen@names@\the\c@refsection}\@empty}
\ExecuteBibliographyOptions{nametracker=context}
\DeclareNameFormat{labelname}{%
\cbx@ifnameseen{\thefield{hash}}
{\ifcase\value{uniquename}%
\usebibmacro{name:family}
{\namepartfamily}
{\namepartgiven}
{\namepartprefix}
{\namepartsuffix}%
\or
\ifuseprefix
{\usebibmacro{name:given-family}
{\namepartfamily}
{\namepartgiveni}
{\namepartprefix}
{\namepartsuffixi}}
{\usebibmacro{name:given-family}
{\namepartfamily}
{\namepartgiveni}
{\namepartprefixi}
{\namepartsuffixi}}%
\or
\usebibmacro{name:given-family}
{\namepartfamily}
{\namepartgiven}
{\namepartprefix}
{\namepartsuffix}%
\fi}
{\usebibmacro{name:given-family}
{\namepartfamily}
{\namepartgiven}
{\namepartprefix}
{\namepartsuffix}%
\cbx@nametracker{\thefield{hash}}}%
\usebibmacro{name:andothers}}
\makeatother
\begin{document}
\cite{sigfridsson}
\cite{knuth:ct:a}
\cite{sigfridsson}
\cite{knuth:ct:b}
\cite{vizedom:related}
\cite{knuth:ct:a}
\cite{vizedom:related}
\cite{knuth:ct:b}
\printbibliography
\end{document}
The two approaches side-by-side.
