What's the difference between demigod and undergod?

Demigod

Definition:

(n.) A half god, or an inferior deity; a fabulous hero, the offspring of a deity and a mortal.

Example Sentences:

(1) Bowie’s 1973 album Aladdin Sane, recorded between the two North American stints of the Ziggy Stardust tour, was conceived as “Ziggy goes to America”, the rock demigod encountering a place equal to his glamour and madness, from the riots of Panic in Detroit to the Hollywood decadence of Cracked Actor, and the sexual alienation of Drive-In Saturday, the title alone a play on the drive-in movie theatres which even now seem so glamorously foreign to Brits.
(2) When Angelina Jolie and Leonardo DiCaprio signed up to humanitarian and environmental causes, for instance, they were already untouchably glamorous demigods whose lives seemed a million miles away from their fans’, and whose jet-setting activism seemed almost as distant.
(3) He achieved that demigod-like status, at least in Pennsylvania and among Penn State fans.
(4) Cable said: "It is clear that in banks like RBS the demigod status granted to Fred Goodwin prevented any form of credible scrutiny.
(5) The more famous phrase was an invention of Turner's friend, John Ruskin , the critic who made the artist a kind of demigod, championing his every brushstroke.
(6) Produced by Tim Heidecker and Eric Wareheim, veritable demigods of the online comedy scene, 555’s hipster credentials are close to unassailable.
(7) For every weedy Peter Parker or Tony Stark sans Iron Man armour, there are armies of demigods looking ripped in latex and leather, many of them played by people called Chris.
(8) At least it is for Tom Derry, who visits the fenced-off shrine in Detroit’s Corktown neighbourhood every week, in memory of the demigods who once walked here.
(9) Saturday saw Lybke, hungover but still in paunchy Teutonic demigod mode, glad-handing the crowd who were eddying through his gallery.
(10) Ayman Youssef Mansour also received three years, but this time not for offending the demigods of the military but rather for "insulting" Islam , "promoting extremist ideas" and "inciting sectarianism" on Facebook.
(11) Australian actor Chris Hemsworth rounds out the top five with $37m, thanks to his roles as a Norse demigod in last year's Thor: The Dark World and the 2012 $1.5bn box-office megalith The Avengers .
(12) And yet, just as an atheist would argue the universe is all the more beautiful and wondrous when divine intervention is removed from the equation, so Smith found his admiration for Mandela grew as he understood the flesh and blood human being, rather than the demigod.
(13) We’re still waiting to see whether Captain America will use his ability, as yet unmentioned in the films and unknown to Cap, to wield Thor’s hammer – and with it the demigod’s power.
(14) He achieved a sort of demigod status in the state, where his 2015 escape was greeted with celebratory gunfire and choruses of narcocorridos (songs lionizing narcos).