here are some synonyms; determined, full of determination, hell-bent, committed, unswerving, unwavering, undeviating, resolute, purposeful,
set, fixed, devoted, dedicated,
uncompromising, persevering, tireless, tenacious, persistent, pertinacious, indefatigable;
obsessive,
fanatical, dogged, monomaniacal; obstinate,
stubborn, unyielding, intransigent, pig-headed,
inflexible, obdurate
http://www.oxforddictionaries.com/us.../single-minded
the bolded can easily be applied to the scenario with hephaestus