Dark Spider-Man (Mac Gargan/Venom II)

Of all the derelicts that comprised Osborn's Dark Avengers, Mac Gargan was certainly the one with the longest history with Norman.  Being mutual foes of Spider-Man, Osborn and Gargan crossed paths on a handful of occasions.  Osborn even used Gargan as his close confidante to communicate information to Peter Parker when Osborn was locked up in prison.  This event is covered more thoroughly here.  

Soon after Gargan would bond with the Venom symbiote...

Ironically Gargan's upgrade pissed of Osborn...because he had his own plans for Gargan as Scorpion.

To say the least, they had a complicated relationship...

Nevertheless, Gargan and the rest of the Sinister Twelve were integral in Norman's plan to ruin Peter's life.  They distracted Peter while Norman abducted Mary Jane.

Spider-Man would eventually defeat both Norman and Mac...with a little help from the Avengers.  

Redesigning Gargan's costume and weaponery is apparently a habitual task for Norman.  When Gargan was placed on Norman's Thunderbolts team, they ran into a bit of trouble as Venom came into contact with Anti-Venom (aka Eddie Brock).  Gargan's Venom suit was compromised and Norman was able to fix him and give him a bit of an upgrade in Amazing Spider-Man #572.  This is covered more thoroughly in the New Ways to Die chapter. 

Osborn created the Scorpio-Venom...The Scorpion's tail was the perfect mechanism for delivering Norman's newly created Super Venom (aka, the Anti-Anti-Venom) serum into Brock.  

Gargan was able to inject Brock but the serum did not completely eliminate the Anti-Venom symbiote from Eddie.  Spider-Man was once again able to hamper Osborn and Gargan's plans.

Of course Gargan and Osborn weren't always on the same team, in fact they started out quite the opposite.  Gargan worked for Obadiah Stane to steal plans from Osborn back in the day.  Gargan's former work came back to bite him in the ass during his days with the Thunderbolts.  Whirlwind and three other D-list villains attempted to blackmail Gargan in order to coerce him to work against his new boss (aka Norman Osborn).  

Gargan didn't let Whirlwind get the best of him though as he helped Norman to squash the blackmailers in Thunderbolts: Reason in Madness.  Gargan and Osborn had a newfound respect for each other.  

Since Gargan was a loyal member of Osborn's Thunderbolts he became the obvious selection for the role of Spider-Man on Osborn's Avenger's roster.  He had to make one small change to join the team; he needed to convert the grotesque Venom into the traditional Spider-Man.  Osborn once again helped to redesign Mac's villainous look...

In that sense, both Gargan and Osborn got a nice dig at Spider-Man by stealing his likeness to push their agenda.  A subtle little payback if you will...  

As a member of Osborn's Avengers, Gargan/Venom was utilized mostly in the interrogation room as one of Norman's torture devices...

Rap Sheet:
1.  Alongside Ares, Gargan helped capture Bucky-Cap and the Black Widow when they infiltrated H.A.M.M.E.R. facilities.  Summarized here.
2.  After Clint Barton's failed attempt on Osborn's life, Gargan was used to coerce Barton into giving up the location of his fellow Avengers.  Summarized here.
3.  Gargan was also 'helpful' in recovering Luke Cage's stolen baby at the conclusion of the Skrull Invasion.  Gargan tortured Skrulls so that they would provide information regarding the Skrull-Jarvis' whereabouts.
4.  Gargan battled Colossus during the confrontation between the X-Men and the Dark Avengers.
5.  Spider-Man kidnapped Gargan and locked him away so that he could infiltrate Osborn's Avengers Tower disguised as Venom.  Spidey's ploy would eventually get busted.  Summarized here.
6.  In a rather gruesome tale that best exemplifies the difference between the Mac Gargan Spider-Man and the real Spider-Man, a thankful man returns to the rooftop of a building where he had attempted suicide a few years back.  The real Spider-Man caught him with a web-net to prevent the fall from killing him back then, when he returned to building the Avengers jet blew by knocking him from the ledge.  This time the Mac Gargan Spider-Man was there to witness, but instead of saving the struggling man, Gargan enjoys watching the man struggle then fall to his death.  A sick man indeed, this was featured in The Amazing Spider-Man Family #8.

7.  During a battle with the Mighty Avengers, Gargan was reverted to his old villainous form in front a variety of news cameras.  Fortunately for him though, no detrimental ramifications ensued because of it.  Summarized here.

8.  After recently elected Mayor J. Jonah Jameson requests Osborn's help to provide him with a 'hero', Norman sends Gargan to fill the order.  Jameson claimed New York 'needed a hero' and he requested Ms. Marvel but soon decided to embrace Osborn's Spider-Man.  

So Gargan initiates a gang war so that he can end it publicly and win some popularity for the new Mayor.  Of course Gargan's less than standard combat tactics are eventually captured in a series of photographs and sent to Jameson.  Jameson then confronts Osborn saying that he no longer wants to be associated with his Spider-Man. 
Osborn then counters with a new plan, he has Bullseye and Daken dress up in their old costumes and attack Mayor Jameson's Big Apple Festival.  Gargan then plays the role of hero defeating the duo and garnering some support for him as a hero.

Fate as one of Osborn's Avengers:
Gargan's run as an Avenger came to an end during Osborn's attack on Asgard.  Fittingly, he was defeated by Spider-Man along with Ms. Marvel and sent into S.H.I.E.L.D. custody.  

Shortly after, the Venom symbiote was removed from his body and placed onto Flash Thompson, who became a government operative.  Gargan was subsequently broken free from the Raft by Alistair Smythe, who fitted him with a new Scorpion costume...so Gargan was there and back again!

As an interesting side note regarding Norman's family life, it is well documented on this site that Norman's youth was filled with abuse from his father.  It is quite likely that Norman's relationship with his mother was painful as well, since he watched her also be abused by his father.  

One can imagine that Norman kept her very close to his heart and any disrespect toward her would not be tolerated.  Here's a panel of Mac Gargan about to crack a 'mom' joke toward Osborn...Norman was less than enthused... 

So, in summary...