I want a custom biblatex cite command that prints first last (year) where first is author's first name last is authors last name and year is publication year.
The following questions have got me on the right track, but since they don't explain what is going on I can't figure out how to edit these custom definitions to suit what I need:
Citing author's full name in biblatex
EDIT: MWE with answers below:
\documentclass{report}
\usepackage{epigraph}
\usepackage{blindtext}
\setlength\epigraphwidth{8cm}
\setlength\epigraphrule{0pt}
\usepackage{etoolbox}
\makeatletter
\patchcmd{\epigraph}{\@epitext{#1}}{\itshape\@epitext{#1}}{}{}
\makeatother
\usepackage{filecontents}
\begin{filecontents}{mytestbib.bib}
@UNPUBLISHED{mumford:quote,
author={Mumford, David},
title={ICM 2002 plenary talk},
month={9},
year={2002}
}
\end{filecontents}
\usepackage[backend=biber, style=authoryear]{biblatex}
\addbibresource{mytestbib.bib}
%% From https://tex.stackexchange.com/questions/24979/citing-authors-full-name-in-biblatex
\DeclareCiteCommand{\citeauthorfirstlast}
{\boolfalse{citetracker}%
\boolfalse{pagetracker}%
\DeclareNameAlias{labelname}{first-last}%
\usebibmacro{prenote}}
{\ifciteindex
{\indexnames{labelname}}
{}%
\printnames{labelname}}
{\multicitedelim}
{\usebibmacro{postnote}}
%% From @moewe
\DeclareCiteCommand{\citetwfn}
{\DeclareNameAlias{labelname}{given-family}%
\boolfalse{cbx:parens}}
{\usebibmacro{citeindex}%
\iffirstcitekey
{\setcounter{textcitetotal}{1}}
{\stepcounter{textcitetotal}%
\textcitedelim}%
\usebibmacro{textcite}}
{\ifbool{cbx:parens}
{\bibcloseparen\global\boolfalse{cbx:parens}}
{}}
{\usebibmacro{textcite:postnote}}
\begin{document}
\chapter{Introduction}
\setlength{\epigraphwidth}{0.5\textwidth}
%% solution from @gusbrs
\epigraph{``The world is continuous, but the mind is discrete.``}{---\textup{\citeauthorfirstlast{mumford:quote} (\cite*{mumford:quote})}}
%% solution from @moewe
\epigraph{``The world is continuous, but the mind is discrete.``}{---\textup{\citetwfn{mumford:quote} }}
%% solution from @moewe
\AtNextCite{\AtEachCitekey{\DeclareNameAlias{labelname}{given-family}}}
\epigraph{``The world is continuous, but the mind is discrete.``}{---\textup{\textcite{mumford:quote}}}
\blindtext \textcite{mumford:quote}.
\printbibliography
\end{document}

\citeauthorfirstlast{key} \cite*{key}, where\citeauthorfirstlastis as defined in the link you provided. Of course, this is not a "custom cite command", but gives the desired result quite conveniently. – gusbrs Mar 16 '17 at 23:55biblatexdetails (but embeded in a full, but minimal.texfile). – jon Mar 17 '17 at 03:50