As Portia's father is dead before the play begins, our primary knowledge of him must come from the contents of his will and what they say of his values and his love for his daughter. He stipulates that his daughter's suitors must choose between three caskets and he who chooses correctly wins Portia's hand.
The caskets are of gold, silver and lead. The correct casket is the one of lead. The very fact of their composition lets us know that Portia's father is not interested in men seeking fame and fortune or those pursuing greed or vanity. He knows that his daughter is worth more than these worldly goals.
Each casket also has a clue indicating its contents. Portia's father has carefully composed each clue to have more than one meaning and thus further weeds out the competition for his daughter's hand by forcing each suitor to reveal more about their own characters in how they choose. Clearly her father is a man who deeply loves his daughter and wants her to spend her life with a man who thinks with his heart rather than his head.
The first suitor chooses the gold casket with the clue, "Who chooseth me shall gain what many men desire." The Prince of Morocco (first suitor) interprets this to mean that the object of desire is Portia. But what does this say about him? It reveals his greedy, acquisitive nature. It also reveals that Portia's father does not see her (or perhaps even all women) as objects of desire to be owned or conquered. Rather he values his daughter for her intelligent mind and ability to think critically, thus he wants a potential husband to see her in the same way.
The second suitor, the Prince of Arragon, chooses the silver casket which comes with the clue, "Who chooseth me shall gain all he deserves." This prince's choice reveals his vain nature and absolute lack of humility. More is revealed about Portia's father here. He seeks a humble man who will appreciate the special qualities of his daughter and not treat her merely as an appendage by which he can look good to others.
Ultimately, the correct choice is made by Bassanio, already the beloved of Portia. He chooses the lead casket, which has been passed over by the others due to its lowly nature and looks. The clue is, "Who chooseth me must give and hazard all he hath." By Portia's father's standards, the man who chooses this casket is indeed worthy of his daughter and her considerable fortune. This man will be willing to sacrifice selfish, self-seeking motives in order to be an appropriate steward to his daughter's future.
Another aspect of the play that particularly reveals Portia's father is her famous discourse on mercy;
"The quality of mercy is not strain'd.
It droppeth as the gentle rain from heaven
Upon the place beneath. It is
twice blest:
it blesseth him that gives and
him that takes."
Portia has been carefully raised by a kind, caring, educated father who instilled the values of faith and humility in her along with the intellectual capability of winning carefully constructed arguments. It can be construed from Portia's life and from the will her father left behind that he was a man of integrity and honor: a proud father and a deep thinker.