"Umbridge just lurked in the corner making notes on a clipboard. You know what Flitwick's like, he treated her like a guest, didn't seem to bother him at all."
--Fred to Harry and Hermione (OP15)
“No! You’ll do no more murder at Hogwarts!”
--Filius Flitwick to Snape (DH30)
Filius Flitwick is the Charms professor at Hogwarts, and the Head of Ravenclaw House. He is very small in stature (he needs to stand on a pile of books to see over his desk), but not small in magical ability. He was an accomplished wizard and, according to rumor, was a dueling champion when he was younger (CS11). Flitwick is an emotional fellow. When Ginny Weasley is taken into the Chamber of Secrets, he bursts into tears. He seems to have a gentle spirit. His office was on seventh floor, near the base of the West Tower (PA).
When Severus Snape became Hogwarts Headmaster, Flitwick stayed to teach. Later, however, when it seemed that Harry needed protection, he joined McGonagall in an attack on Snape (“You’ll do no more murder at Hogwarts!” -DH30) that forced him to abandon his position at Hogwarts.
When the news came that Voldemort and his army would attack Hogwarts in early May, Flitwick constructed intricate magical defenses, and then took groups of fighters up to the three highest towers to work spells from above. When the battle was at its fiercest, Flitwick fought Yaxley and may have killed Dolohov.
Flitwick had taught students how to “swish and flick” at Hogwarts since at least the 1970s and was well-respected by everyone, from Dumbledore, to Malfoy to McGonagall to Dolores Umbridge.
Charms, duelling (if Lockhart is to be believed)
Other canon notes and references
Interests: decorates with live fairies quite a bit.
Drink: cherry syrup and soda with ice and an umbrella. (apparently doesn't drink alcohol?)
Filius (JKR) is Latin for "son."
Flitwick sounds a lot like his wand-waving advice "Swish and Flick." Flitwick is also a town in Bedfordshire, on the River Flit (Wikipedia). The Anglo-Saxon place suffix -wick means "dwelling or farm" (CountryLovers Placenames).
Rowling was surprised by the elfin appearance on Professor Flitwick in the films; she had imagined him a small but otherwise typical-looking elderly wizard (JKR).