Many were confused on who the hell Helman was. He didn't have any significant bio nor models. Many veteran Warhammer gamers and lorefags scratched their heads over who he was until they managed to find him in the flavor text of the Corpse Cart (thus making him a case of Ascended Extra if one were to use TVTropes slang). But if those so called 'lorefags' were really 'lorefags' they should have known that Helman Ghorst was part of the campaign Sigmar's Blood, where he got an extended background from Phil Kelly.
Helman used to be in the past a pretty nice guy, youngest of the five brothers Ghorst and who lived in the village that would later on be known as Castle Templehof. He used to work, like his father, as a farrier and groom. Helman was a thrill seeker, taking any job that required him to traverse the treacherous roads of Sylvania. He loved his brothers even more though, always returning home to see them again.
One day however he experienced tragedy.
His family fell to the Plague of Blue Roses. He embraced them in order to die, yet the plague had no effect on him. This was what caused him to study the dark arts of necromancy and trying to get his brothers resurrected, yet the Witch Hunters smelled him out and he fled with the corpses of his family to Sylvania where he managed to meet Mannfred.
At first the vampire wanted to kill him for trespassing on his land, but he quickly discovered that offing Helman would be a waste, so he took in the young Ghorst as his disciple.
Now a necromancer wielding the Liber Noctus and commanding his undead host from atop of the Brothers Ghorst Cart that is pulled by his deceased family.
Officially, no one knows what became of Helman Ghorst. It’s likely he was killed at the end of the Sigmar’s Blood campaign though it’s left vague enough to where he and his brothers could very well still be alive and continued to serve the last of the Von Carsteins till the very end.
On the Tabletop
On the tabletop Helman Ghorst is a Level 2 Necromancer with a hand weapon and the Cursed Book. He always gets the spells Vanhel's Danse Macabre and Gaze of Nagash, and he cannot even swap the spells out. He's also on a Corpse Cart pulled by his brothers (in practical terms, it hits at Strength 4 instead of Strength 3). Whoopee.
If this seems odd to you, then that's because Ghorst was given a fucking massive power boost in TW:WH.
Gameplay and Capabilities
Helman is quite useful in many ways and originally outperformed Heinrich Kemmler (the poor dude eventually caught a break and became great). If he becomes the guy you pick up at the beginning of the Grand Campaign/Mortal Empires, then all armies get a bonus to unit replenishment and everyone in his army gets poison attacks. His other abilities is that instead of the raising zombies like Kemmler and other Necromancers, he can raise GRAVE GUARD instead, and his Grand Campaign abilities that he can unlock allow him to increase the research rate of the Vampire Counts (which also stacks with his Neophyte trait, allowing to get double from him), can buy a trait that further decrease the costs of raising troops (and which stacks with the one trait all Vampire Counts characters have, which makes raising for him new regiments dirt cheap). In addition, Helman can unlock at level 15 the Brothers Ghorst Corpse Cart (though sadly it cannot be upgraded to have a Balefire Brazier or Unholy Lodestone).
Unfortunately, his Corpse Cart makes him a very slow and easy target as he is unable to disengage with any speed or hide in a unit.
Later patching added a sexy and significant +30% research bonus for playing Ghorst to help him play catch up... and then he was also given hilariously rather useless bonuses to corpse cart recruitment ranks and charge bonuses (only technically useful considering corpse carts are units that just stand in the back giving buffs). Even later, he got the margonally more useful "Lesser Raise Dead" power on corpse cart units in his faction, though not on mounts for Necromancers, which this fa/tg/uy supposes makes him more useful at spamming tarpit horde armies led by Master necromancers, but... It is a bit of a buzz kill to see him and his necromancer lords and heroes lack an altogether useful bound spell.
Additionally, the changes to summons that causes them to disappear after a set duration instead of degrading over time made him even worse, as the greatest strength of grave guard is their ability to get in the way for a very long time, but that doesn't matter when they just poof out of existence.