Bowser is strict, mean and somewhat rude. At times he can be truly merciless, such as when he burned Bowser Jr in flames for not doing well in school in First episode. He can also be very immature as he told Junior to "get a life". However, he can also be truly compassionate too, like in the end of Living with Nerdy when he sweetly forgives Bowser Jr for understanding the depth of his mistake. He is somewhat knowledgeable, but can also be very immature and snap just at the thought of something he doesn't like (like his rival Mario). He shifts from just a villain to a caring father throughout the series.
Bowser is currently the strongest known character in the series, greatly and feared for his power by generally all characters. His most used power is his fire breath, which he uses for attacking and threatening. He also has enough strength to break down walls, and glass in Rise of Fawful.
Bowser's interests are not expanded upon in the series, but he seems to be sort of self-absorbed as seen inLiving with Nerdy where he passionately hugs a statue of himself.