Here, using Warduke's stats, is an illustration of just how much D&D sourcebooks have changed over the years.
His first appearance was an entry in 1983's The Shady Dragon Inn:
"WARDUKE wears a suit of half-chain and a black, winged helmet. His shield bears the sign of a demon's head. He was an old friend of STRONGHEART Good Paladin's, but now the two are enemies. Both were exposed to the Heartstone, and WARDUKE's cruel nature was brought out while STRONGHEART's just nature became stronger. WARDUKE is a friend of SKYLLA's and wears a demon device like hers. These two plan to overthrow Kellek once all good fighters are beaten. WARDUKE captured an evil Nightmare for his mount, and it frightens many of his enemies. WARDUKE especially hates STRONGHEART, who he feels wastes his time protecting the weak and helpless. "A true fighter," WARDUKE feels, "makes himself rich and powerful by the strength of his sword arm. He takes what he can - if you would keep your possessions, kill those who seek to take them." He calls his sword "Nightwind.""
And his most recent, in 2021's The Wild Beyond the Witchlight:
"Warduke's services as a remorseless killer for hire can be easily bought. The evil swordsman serves Kelek as a chort and adventuring companion from time to time. He isn't terribly bright, which is why he leaves the plitting and scheming to others.
What does Warduke look like under his dread helm? No one knows. He never removes his helmet to reveal his face to others, but the visage benath it is that of a grim, hideously scarred gladiator."
We've come a long way, baby!
You know, sometimes it's nice to have a villain who does evil things simply because they get him what he wants, rather than some deep, tragic backstory.
I can completely understand Warduke's motivations. He's strong, he feels that being strong means that he can take what he wants, and he feels that anyone who can't defend their own property with their own two hands doesn't deserve it.
What makes good characters, I think, is whether or not he's one of those "oh, I'm beaten so by my own values I deserve to lose my property"-types, or one of those "No! No! This isn't fair!" hypocrite types.
The 2003 version specifically suggested using him as a way to smack down any players who thought they were too badass for regular enemies to be any sort of threat. His abilities included restoring his own hit points like a videogame boss going into a second life bar, and the tendency to teleport away from battle when he was on the verge of being defeated, so he could heal up and come after you again...
Ah, so kind of like Venger, then? That makes sense. His design just screams "boss battle". I especially like that "teleport away from battle on the verge of being defeated". It feels very "classic villain" like Venger himself or Doctor Doom.
I'm also kind of reminded of that Shadow of Mordor game where if you don't finish off an Orc Captain, they might pop up again hoping for payback, or will recognise you and try to actively hunt you down.
Just keep in mind the greatest weakness of every D&D villain: A small, square room with no terrain and no henchmen. 5th Edition forces you to use your head if you want your bad guy to be a challenge for the players, just like it forces players to use their heads to take down strong opponents. If you haul him in on a 5th-level party (he's challenge level 5) and expect that's all he needs, he'll get dogpiled and steamrolled. But if you design the encounter so his henchmen bog everybody down and the terrain keeps them off him so he can use his specialty - targeting individuals and moving in for the kill - then you've got a good fight going.
Warduke's Second Wind will buy him like... one more hit. Keep that in mind, and make sure he has room to back off and heal himself without taking another hit in the process.