Romeo is an exceedingly complex character with an enormous range of emotions. As a result, Romeo provides an immense challenge for any actor attempting to portray him.
Romeo is born into the Italian nobility - specifically, the eminent Montague clan. He has a personal servant, Balthasar, and is notably skilled with a sword, indicating prior training in fighting technique, likely as a result of his family's dominant socio-economic status. Physically, he is described both by Juliet and the Nurse as being exceedingly handsome.
At the beginning of the play, we see Romeo as an unhappy individual. He is apt to spend much time alone, wallowing in his own sadness. However, though he is portrayed as a depressed individual, we know otherwise when his friends, Mercutio and Benvolio all say that he has changed and is not the boy he used to be before his infatuation with Rosaline. Like many young men his age, his primary concern is love, and Romeo reacts very poorly to rejection from a potential lover, as exemplified by his unrequited love for the fair Rosaline.
Romeo is not antisocial in nature, however - he has close relationships with both his cousin, Benvolio, and Mercutio, a kinsman to the Prince. When confronted by Benvolio, Romeo acknowledges his pathetic behavior:
"I have lost myself, I am not here. / This is not Romeo, he's some other where."
However, when Romeo is capable of picking up his spirits, he is a remarkably endearing individual. After meeting Juliet at Capulet's ball, he changes dramatically back to the character his parents, Benvolio and Mercutio have known:
"Now art thou sociable. Now art thou Romeo, now art thou what thou art, by art as well as by nature." - Mercutio (II.4.87).
His witty, back-and-forth dialogue with Mercutio indicates a potent sense of humor, a feeling of playfulness, and a significant, innate intelligence. His monologues to Juliet also demonstrate an extraordinary proficiency with language, particularly with his poetic expressions of passionate love, which have been rivaled by few in all of history. Romeo is also fiercly loyal to those who are close to him - as it turns out, loyal to a fault.
Despite the fact that he ultimately slays three people (including himself), Romeo appears to have a disdain for killing. He feels alienated by the familial feud between his family and the Capulets:
"Why then, O brawling love, O loving hate, / O anything of nothing first create!...This love feel I, that feel no love in this." (I.1.181)
This becomes more pronounced when his family's hate denies him access to loving Juliet. In a world engulfed by hate, Romeo, like Juliet, values love above all else, and is willing to both risk and sacrifice his life for love. Romeo is the archetypical Petrarchan lover, idealizing his women as pure, chaste, and beautiful past compare.
Romeo is a character whose emotions are played out to their fullest extremes, and this is true for his more negative qualities as well. Romeo, like all Shakespearean heroes, is a flawed character. He is highly impulsive, and is incapable of controlling his emotions in seemingly any circumstance. Instantaneous onslaughts of passionate emotion can temporarily blind him from reason and drive him to perform acts of cathartic insanity, such as his murders of Tybalt and Count Paris, as well as his own suicide.