My three favourite Lone Wolf Heroes are all men who are broken in ways you think would make them irreparable, isolated (even amongst friends and family) and all wonderfully, horrifically violent. All these stories are easily 5 star reads for me, by authors I love, and with a storyline that keeps me going back for more.
When it comes to your heroes, if you are of the ethos: The Badder, The Better, I cannot think of any alphas you could love more.
Ladies & Gentlemen, I give you my beautiful beasts...
Wolf (The Henchmen MC #3) by Jessica Gadziala
How broken? Wolf talks in mostly single syllables, has seen terrible abuse at the hands of his father, and gets sent in to do the worst of the dirty work for what is already a pretty dirty MC.
How violent? When your MC consists of killers and hitmen, and even they want you locked down in a shed... you may have anger-management issues. To fully appreciate all the vicious goodness that is Wolf, I recommend reading Reign & Cash first.
Souls Unfractured (Hades Hangmen #3) by Tillie Cole
How broken? Haunted by a hideous past, a father that sucked so bad I almost couldn't read those parts, and still torturing himself (literally and physically) decades later. And he's a cutter.
How violent? As violent as you could probably get without superpowers. To see him in all his monstrous glory, read It Ain't Me, Babe and Heart Recaptured first.
Lover Awakened (Black Dagger Brotherhood #3) by J.R. Ward
How broken? Centuries of torture & abuse. Reading about what he went through was just shockingly sad.
How violent? If Flame was as violent as you could get without superpowers, Zsadist is Flame on superpower-crack. For the full paranormally disturbing effect, read Dark Lover and Lover Eternal first.