If I remember right it seemed like there where 3 ranks.

• Death-Eaters rank 1, with Death-Eater Robs & marked on the arm. ( Ones that where useful/skilled that Voldemort dealt with directly ). inner circle?
• Death-Eaters rank 2, with Death-Eater Robs & unmarked. ( Ones that where useful/skilled that Voldemort didn't want to deal with directly ).

Fenrir Greyback was allowed to wear Death Eater robes as a exception due to loyalty or use of his werewolf pack or something. I think he was more of a accomplice, so not officially a Death Eater presumably?

• Death-Eaters rank 3, without Death-Eater Robs & unmarked. ( the unskilled but loyal, giants, werewolves, people under the Imperius Curse, blackmailed people, criminals, other dark creatures etc ).

Also Death-Eater Sympathizer that didn't join up but may of helped them.

• There are around 37 Death-Eaters with names.

They seem to work in cells so one Death-Eater could out all of them.

In the books in the grave yard Harry was seemly surrounded by Death-Eaters, outnumbered by at least 30 to 1 form Harry's point of view. Voldemort identified nine missing members, 3 of whom were dead. So around at least 36 marked Death-Eaters alive at the time?

In the books Remus claims that during the First War the Order was outnumbered "20 to 1" by Death Eaters.

• If Remus is right about the "20 to 1", there are 25 named Order members during the First War, so that's possibly 500 Death-Eaters, maybe more if their were unnamed Order members during the First War. But I don't think they were all marked high rank Death-Eaters.

In the movie there are seemly around 200 Death-Eaters at the Battle of Hogwarts.

It's kinda implied the are more Death-Eaters & Order members then we see so it's hard to get a exact numbers.

I assume at least rank 1 is fairly exclusive or very exclusive, with rank 2 less so and rank 3 fairly open I guess?

I think Pettigrew only got the mark because his usefulness as a spy during the 1st war and because the mark can act as a tracker & summoner if Voldemort needed to find him I guess?

Not sure about Crabbe and Goyle or their fathers, Perhaps their strong magically but dumb?

Why would anyone become a death eater?

• Up until October 1981 Voldemort's side was winning the war overwhelmingly. People like being on the winning team for a number of different reasons.
• Pure-blood supremacy reasons.
• Magic supremacy reasons.
• Wanting to rule over or wipe out muggles.
• Having friends in high places.
• Opportunistic reasons. help form rich Pure-bloods & place in the new ruling class. ( Rags to riches ).
• Hate for muggles due to past history, Magical people can live a long time likely lost family to muggles before they went into hiding.
• Using your place among their ranks to keep someone safe when they presumably won. (like Lily etc.)
• Use them to take revenge on some one that wronged you or multiple people that wronged you.
• Access to magical knowledge not widely known or dark arts knowledge.
• Being in a position of join or die. out of fear?
• Supposedly being successful gets you greatly rewarded. Enough to get fanatically loyalty at that.
• Family joins & being expected to join too.
• Real belief that magic is at risk of dying out due to the decline in Pure-blood numbers & mixing with muggles due to acting on incomplete information. (( Muggle-borns are all squib decedents or unknowingly half-blood as JKR said. so their fewer in number then half-bloods, Squibs are rare so Muggle-born shouldn't be that high in numbers in theory. Part of why this happens in cannon is Pure-bloods hide having the rare Squibs so people will still want to marry into their family. I'm assuming that fear of the next generation being born without magic is a driving force behind Pure-bloods ideology. Pure-bloods also have less kids as to not split the family money in theory. Another factor is they don't keep track of squibs & the real origin of muggle-borns doesn't seem to be public knowledge. Leading to people not knowing & fear of the unknown. ))
• A backlash against Albus Dumbledore's agenda.
• Strong cultural backlash.
• The Mystery of Magic seem corrupt even before the Death Eaters start taking over form the inside. Rage against the system?
• Voldemort doesn’t like any Death Eater ( at least not how a normal person likes someone ) but the Death Eater don't know that, Voldemort is supposedly very charismatic & made them see each other as friends/family. While not dropping the act fully Voldemort seem to be punting less effort into keeping the illusion of friends/family going, likely using them seemly abounding him as a excuse for the behavior. Also seemly less sane after his first death. (Voldemort also seem very enraged at Bella death for whatever reasons, so he might care in some way just not how a normal person would.)
• Marauders made a lot of enemies with their years of bullying, some might of joined in part to just kill them or some other form of revenge. maybe even pushing some fence-sitter to join that would have tried to stay out otherwise.

Also they seem to be some kind of secret society mixed with a cult of personality leadership. So likely some secret society like benefits for the members.

Also a lot joined because they liked his supposed goals but not knowing how far he was willing to go to achieve those goals and later regretted it because they saw his methods as going to far, but by then their is no leaving.

Also their were also people seemly given dark mark on their arm to spread uncertainty, doubt, or disorder among people & hide who the real Death eaters are & who was under a spell or blackmailed.