In the beginning of this mock-epic, Pope declares that a "dire offence" (Canto 1 line 1) has been committed. A lord has assaulted a "gentle belle" (line 8), causing her to reject him. He then proceeds to tell the story of this offence.
While Belinda is still asleep, her guardian Sylph Ariel forewarns her that "some dread event impends". Belinda then awakes and gets ready for the day with the help of her maid, Betty. The Sylphs, though unseen, also contribute: "These set the head, and those divide the hair, some fold the sleeve, whilst others plait the gown" (146â147). Here Pope also describes Belinda's two locks of hair "which graceful hung behind". The Baron, one of Belinda's suitors, greatly admires these locks and conspires to steal one. Building an altar, he places on it "all the trophies of his former loves" (line 40), sets them on fire and fervently prays "soon to obtain, and long possess" (line 44) the lock.
Ariel, disturbed by the impending event although not knowing what it will be, summons many sylphs to him and instructs them to guard Belinda from anything that may befall her, whether she "forget her prayers, or miss a masquerade, Or lost her heart, or necklace, at a ball" (line 108â109). So protected, Belinda arrives at Hampton Court and is invited to play a game of ombre.
The conspiring Baron acquires a pair of scissors and tries to snip off one of her locks but is prevented by the watchful Sylphs. This happens three times, but in the end the Baron succeeds (also cutting a Sylph in two although Pope reassures us, parodying a passage in Paradise Lost, that "airy substance soon unites again" [line 152]). When Belinda discovers her lock is gone, she falls into a tantrum, while the Baron celebrates his victory.
A gnome named Umbriel now journeys to the Cave of Spleen and from the Queen receives a bag of "sighs, sobs, and passions, and the war of tongues" (canto 4 line 84) and a vial filled "with fainting fears, soft sorrows, melting griefs, and flowing tears" (line 85â86) and brings them to Belinda. Finding her dejected in the arms of the woman Thalestris, he pours the contents over them both.
Many people, moved by Belinda's grief, demand the lock back, but the Baron is unrepentant and refuses. Clarissa admonishes them to keep their good humour, but they will not listen and instead a court battle ensues between the nobles, with glares, songs and wits as weapons. Belinda fights with the Baron and throws snuff up his nose to subdue him. When she demands that he restore the lock, however, it is nowhere to be found. It has been made a constellation and is destined to outlast the contestants.

Question: What sort of mythical creature is Umbriel?
Answer: A  gnome.
Alternative answer: a gnome