The character Malvolio (meaning literally "I mean ill will) is immediately affected by the implications of his name. His personage is implied directly to be one of negative and somewhat disagreeable nature, which is continued and supported throughout the play, leading to his downfall and mockery which both initially seem to be thoroughly deserved, due to his numerous defects of personality.
The first evidence of Malvolio's undesirable disposition comes with his own first appearance in the play during which he makes a point of insulting the wit and intelligence of Feste "I marvel your ladyship takes delight in such a barren rascal". Through doing this he shows himself to be man who condescends to those that he believes to be lower than him in any way, by acting on his own personal belief of superiority, and this later becomes a major player in his downfall.
Initial impressions are supported by further vices in Malvolio's general character and these lead to further aversion to him. He shows himself to be a strict puritan and this is also suggested by the opinion of Maria "The devil a puritan that he is". He denies himself indulgences and pleasure whilst at the same time begrudging these things of others. He makes a point of taking the moral high ground over Maria, Feste and more importantly, his social superior Sir Toby, when he scorns them for their revelries and "disorders". This in turn adds to their desire to avenge him and bring him from his level of false authority, back to his true social class of a mere steward at which he is unable to give out orders, but only to receive them.
Although he is a man of supposed purity and self-denial in practise, his aspirations are such that he becomes hypocritical. In turn he makes his character one of further malevolence. He secretly longs for the life of a man higher in social status and fancies...