Nemesor Zahndrekh
"Another fine victory over the crude and the disorderly, Obyron! It seems strange to me that the enemy generals saw fit to loose so many wild beasts upon the field of battle. Their so-called tactics become more desperate and barbaric by the day. So long as we stand tall, old friend, it shall avail them naught. Onward!"
- – Nemesor Zahndrekh, following his victory over a Tyranid splinter fleet
"Even if we all ceased to be flesh and blood millions of years ago, which of course I don’t believe for a moment,’ – Zahndrekh actually winked – ‘wouldn’t it have suited us better to live in denial of that, as some fools might say I had done? Wouldn’t it be better, Obyron, just to accept our fate, and enjoy immortality for the everlasting life of merry campaigning it has proved to be?"
- – Nemesor Zahndrekh to his Vargrad Obyron revealing the fact he isn't as insane as he seems
Nemesor Zandrekh (AKA "that old coot" or "Creedcron") is generally accepted to be the most bro-tier Necron overlord in the galaxy. He's a mix of Creed and Old Man Henderson, with a healthy dose of Don Quixote to go along with it. Among a thousand other commanders who'd rather exterminatus an entire sector just to see their foes dead, old man Zandrekh makes a point of employing only honourable methods of war, giving his foes a chance to surrender, and capturing them alive if possible.
Zandrekh's prisoners can look forward to a pleasant stay at his flagship, having weekly dinners with their captor and witnessing the marvels of Necron culture and technology... until the old coot's bodyguard gets rid of them claiming "they were killed while trying to escape". Speaking of said bodyguard, he's the only other Necron who can stand Zandrekh's company, and has the doubtlessly cool-sounding title of Royal Vargard (regardless that Vargard is the word "Vanguard" with a few letters changed).
Why He's Such A Cool Guy
Well, Zandrekh did not take well to the biotransference process. In fact, it gave him Alzheimer's. As such, he is completely unaware that he's an immortal robot from outer space, and thinks he's still a Necrontyr, from before the Eldar even existed. He's also nearsighted, making him see all of his enemies as Necrontyr rebelling against the Triarchs, which in turn makes him quite a bit less xenocidal than most of his species. Woe the day he finds a pair of glasses, and discovers the green, smelly and burly necrons he keeps meeting around the galaxy are not what they seem. As shown in the newest story containing him and Obyron, he has just been playing the delusional fool and knew all along about the state of the Necrons.
As for the "Don Quixote IN SPESS" aspect, it's actually canon – in the new 8th edition his Transient Madness rule has an effect named "Solarmills ? Charge !" - just with infinitely less Fail, since his tactical acumen was untouched by his delusions. With a generous disregard for reality, a belief that he's still in the past, and a loyal servant who is aware of what's going on yet does nothing to stop him (compare Obyron with Sancho Panza), he's one hardass grandpa.
Troll-tastic
5th Edition Codex
Zandrekh lets you bring as many Deep Striking units as you want during your opponents movement phase when they bring something in from reserve. So use that flyer they have in Ongoing Reserves to trigger a Monolith assault on your opponent's ass and go in dry. You could basically pull off something akin to a Deathwing Assault using this asshole if you're using a fuckload of jump infantry. Heavy Destroyers and Wraiths come to mind, maybe a Tomb Stalker if you have the gold for such a model. If you're playing Apocalypse and have Pylons in Deep Strike Reserve, throw that shit on the table as well. Just throw the most threatening shit you can at them and watch your opponent shit their pants in sheer terror as they have no fucking idea how to respond.
7th Edition Codex
Do you just hate how the enemy sneaks up on you with all these strange special rules that no regular squad of Necron ever would have?
Don´t worry, Zahndekh has a stratagem towards such rules as: Counter attack, Furious charge (mix this one with the Reclamation legion that gives all units within it Relentless, and you see your opponent drop some serious "WTF" then he sees you shoot him and then charge him; nobody expects to see a squad of 10 warriors charge towards a dedicated CC unit), Tank Hunters, Stealth (yeah this guy can make a entire unit of giant robot skeletons hide, go home Creed, given that some other unit also has stealth of course).
And if you can't get a special rule for Zahndrekh and his unit just have to find the thing you want in the warlord traits, he can chose any Warlord trait from the Main book or the Necron Codex and gain it for that turn, so guys if you run this guy learn your Warlord traits.
What about the actual unit? Offensively mediocre, Zahndrekh is one of the most damage-resistant things on the board. Three wounds, 2+/4++, reanimation protocols, WS5, T5, this guy just isn't going away, and you can imagine him contentedly lecturing the frustrated chaos space marine lord the whole time. He's not winning any fights, per se, but with the right warlord traits this wily Necron can hold off a challenge monster a few crucial turns until his squad (or Obyron) can bail him out or win the game. If you find yourself fighting him, don't even bother charging him without dedicated close-combat fighters: Slay the Warlord just isn't worth the trouble, and he'll statistically beat many HQs of similar cost.
8th Edition
8th edition is all about auras. Commanders and leaders projecting bubbles around themselves to buff up their troops so they can actually get their points back. Zahndekh shuts them all down. Well OK only one of them down at a time, and only within 12 inches. But this is still huge. Rules as written, you can shut down Azrael's Lion Helm, leaving the heavy plasma spam he was guarding open for some maximum rape.
On top of that, he gives cool random buffs (taken from a D3 chart) to one INFANTRY unit within 6 inches. And you roll the D3 before you choose the unit to buff, meaning the buff won't absolutely wasted just because of a bad dice roll (it can still be absolutely wasted, just not because of one bad roll). His random effects are +1 Attack, +1 Ballistic Skill, or "I'm Don Quixote! Charge those Solar Mills!" i.e. re-roll failed charges.