Thomas Putnam comes from one of the richest families in Salem. When things have not gone his way, prior to the events in The Crucible, he acted vengefully and only with selfish thoughts. He felt his family was slighted when his brother-in-law was not chosen as Salem's minister. Thomas sued George Burroughs, the man who became minister instead of Thomas' brother-in-law (prior to Parris), for a debt he did not owe.
When the accusations of witchcraft emerge, Thomas jumps on the bandwagon immediately because he is a selfish opportunist. He knows that those convicted will have to sell their land (for less that what it's worth) so he encourages the convictions. The more people are imprisoned or executed, the more land he is able to buy and the more likely he can get back the respect he thinks he deserves. He represents greed and moral indifference. He adds to the hysteria to pursue his own selfish greed whereas others exacerbate the hysteria because of religious fanaticism or mob mentality.
Thomas Putnam persuades Reverend Parris to recognize the presence of witchcraft in his Salem community. Eventually Parris uses his daughter to accuse people of witchcraft whose property he covets.
Putnam is one of the wealthiest men in Salem and holds many grudges against his fellow residents. He is a bitter man and blames the Nurse family for blocking the appointment of his brother-in-law to the ministerial position. Putnam also pushes his daughter to accuse people of witchcraft, including Goerge Jacobs, whose land was available for purchase after execution.
Miller, in a sense, used Putnam as a symbol of individuals of his own time (the era of McCarthyism) who were accusing people of being communist for equally selfish and petty reasons.