Priestly presents the character of Mr Birling as a striking character who likes to voice his opinions. This can be seen when Birling is described as a “heavy-looking, rather portentous man” which gives an impression he looks quite threatening. The adjective ‘portentous’ has the connotations that he is pompous and effectively presented as an unlikable character. I believe Priestly has presented the character this way so Birling can be disliked by the audience and be on an even playing field with Gerald. The adjective ‘heavy’ has the connotations that he is strong and tough.
Birling is portrayed as rather over-confident in his opinions when his mistaken view for the “unsinkable Titanic” which is an example of dramatic irony.