Tom Riddle's gang

"There were half a dozen teenage boys sitting around Slughorn with Tom Riddle in the middle of them, Marvolo's black and gold ring gleaming on his finger."

- The structure of the gang, as seen in Horace Slughorn's memory in the Pensieve

Tom Riddle's Gang was a group of fellow Slytherin students Tom Marvolo Riddle had around him during his time at Hogwarts School of Witchcraft and Wizardry. He claimed they were his friends, and made it appear so in public. In truth, however, he had no attachments for them, as he never once desired a friend, and he only manipulated them to do his deeds, which led to nasty incidents over the years. Through Riddle's intelligent and discreet methods, the gang was never connected to these incidents.

"Tom Riddle nearly smiled as the others laughed again. Harry noticed that he was by no means the eldest of the group of boys, but that they all seemed to look at him as their leader."

- Harry noticing the hierarchy of the gang in the Pensieve memory

Presumably, although the gang disbanded after Riddle graduated from Hogwarts in 1945, it was a precursor to the Death Eater organisation. Indeed, some (if not all) of the members became the earliest known Death Eaters.

Known members
"They were a motley collection; a mixture of the weak seeking protection, the ambitious seeking some shared glory, and the thuggish gravitating toward a leader who could show them more refined forms of cruelty."

- Albus Dumbledore on the the principal attributes of the gang, many of whom would later go on and become Death Eaters. Here is a list of known members:
 * Tom Marvolo Riddle (Leader)
 * Avery Sr.
 * Lestrange Sr.
 * Rosier Sr.(possibly)
 * Mulciber Sr. (possibly)
 * Nott Sr. (possibly)
 * Antonin Dolohov (possibly)

Behind the Scenes

 * Interestingly this group shares many of the same surnames with those who were part of the gang of Slytherins that attended Hogwarts in the 1970s. This is likely not coincidental as those in the latter group may be the children of those in the former.
 * It's unknown what happened to the members of the gang when Tom was abroad looking for followers. It's possible that they traveled with him or they may have simply kept in correspondence with him while remaining in England.

Appearances

 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Half-Blood Prince (video game)