self-possessed (adj.)

• aloof
• assured
• balanced
• calm
• collected
• composed
• confident
• controlled
• cool
• detached
• dignified
• easy
• easygoing
• equanimous
• even-tempered
• forward
• imperturbable
• importunate
• independent
• levelheaded
• peaceful
• placid
• poised
• pushy
• refined
• reserved
• self-asserting
• self-assertive
• self-assured
• self-confident
• self-contained
• serene
• strong-minded
• strong-willed
• together
• tranquil
• undisturbed
• unflappable
• unperturbed
• unruffled
• well-balanced