The two-faced one
Professor Quirinus Quirrell, Defence Against the Dark Arts professor in Harry’s first year at Hogwarts. Walking, talking proof that appearances can be deceptive.

‘Sometimes,’ he said, ‘I find it hard to follow my master’s instructions – he is a great wizard and I am weak –’
Harry Potter and the Philosopher’s Stone

You said it, Quirrell.

The slippery one
Gotcha, Lucius Malfoy. It takes a daring man to lie to Lord Voldemort. Daring or foolish? We’ll go with the latter.

‘My Lord, I was constantly on the alert,’ came Lucius Malfoy’s voice swiftly from beneath the hood. ‘Had there been any sign from you, any whisper of your whereabouts, I would have been at your side immediately, nothing could have prevented me –’
‘And yet you ran from my Mark, when a faithful Death Eater sent it into the sky last summer?’ said Voldemort lazily, and Mr Malfoy stopped talking abruptly. ‘Yes, I know all about that, Lucius … you have disappointed me … I expect more faithful service in future.’
‘Of course, my Lord, of course … you are merciful, thank you …’
Harry Potter and the Goblet of Fire

Merciful. Really?

The most loyal one
Bellatrix Lestrange was hopelessly devoted to You-Know-Who.

‘My Lord,’ said a dark woman halfway down the table, her voice constricted with emotion, ‘it is an honour to have you here, in our family’s house. There can be no higher pleasure.’
Harry Potter and the Deathly Hallows

Her loyalty knew no bounds. No bounds whatsoever, it appeared:

‘You should be proud!’ said Bellatrix ruthlessly. ‘If I had sons, I would be glad to give them up to the service of the Dark Lord!’
Harry Potter and the Half-Blood Prince

We know who’d never receive a nomination for Mum of the Year, then.

The wormtailed one
A lot of people say they’d give their right arm for something or someone they loved. But Peter Pettigrew actually gave his right hand up for the Dark Lord – though he got a shiny new one in the end.

‘My Lord,’ he whispered. ‘Master … it is beautiful … thank you … thank you …’
He scrambled forward on his knees and kissed the hem of Voldemort’s robes.
‘May your loyalty never waver again, Wormtail,’ said Voldemort.
‘No, my Lord … never, my Lord …’
Harry Potter and the Goblet of Fire

It came back to bite – or rather strangle – him, though.

The brave one

‘You think he is mistaken? Or that I have somehow hoodwinked him? Fooled the Dark Lord, the greatest wizard, the most accomplished Legilimens the world has ever seen?’
Harry Potter and the Half-Blood Prince

But actions speak louder than words, don’t they, Severus? And for that, we salute you.