Phlegmatic is an adjective that means having a calm, composed temperament.
You may recognize the word phlegm, as in the bodily fluid, in our word of the day. It turns out there is a connection. So how did phlegm come to be associated with a synonym of ‘calm’ and ‘stoic?’ The answer goes back to the ancient Greeks. They believed that human personalities were controlled by four bodily fluids called humors: Blood, black bile, yellow bile and phlegm. Those ruled by phlegm were thought of as calm and unemotional. Centuries later, we would refer to such people as ‘the phlegmatic type.’
Charlie’s phlegmatic personality made him an ideal person to be around in times of crises. No matter how crazy things would get, he would remain cool and unemotional.