Answer
I am not fully aware of all the details, but he was certainly a son of Drona and is described as having certain brahminical or mystical powers.
However, by taking the side of Duryodhana in the Battle of Kurukshetra, his consciousness became contaminated. He developed the mentality of enmity toward the Pandavas and repeatedly attempted to harm them, sometimes even through unjust means.
This tendency to harm pure devotees is considered a serious flaw. Pure devotees of the Lord cannot ultimately be destroyed, but those who are materially inclined often fail to understand their elevated position and become envious of them.
Although he attempted to kill the Pandavas, he was ultimately defeated in the battle of Kurukshetra by Arjuna.
Regarding his classification as a chiranjeevi, I am not sure of the scriptural basis for that description. According to the Bhagavad-gita, all living beings are eternal in the sense that the soul is never destroyed. We are all eternal spirit souls, and in that sense no one actually “dies.”
Therefore, I am not familiar with the specific usage or classification implied by the term chiranjeevi in this context.
