性子

This horse has a fierce temper and is very difficult to subdue.

My brother's got a fiery temper and flares up at the slightest provocation.

The child is acting on impulse and insists on going to the zoo.

a stubborn temper

have a good/bad temper; be good-/bad-tempered

have a sluggish disposition

fiery temper

violent/hot/quick/raging temper

be hot-tempered/short-tempered

allow a loose rein to one's temperament

get into a temper

keep/control/hold/gather one's temper

The drug is mild.