SEOUL, South Korea — When North Korea held a state funeral for its leader, Kim Jong-il, in 2011, one son was conspicuously absent.

The absence of Kim Jong-nam — the eldest son of the family, who was bound by Korean tradition to preside over the funeral — was all the evidence outside analysts needed to see how isolated he had become from the center of power in North Korea, the world’s most secretive regime.

Never fully accepted by his family, sidelined by his powerful stepmother and haunted by fears of assassins, Mr. Kim lived much of his life wandering abroad, in Moscow, Geneva, Beijing, Paris and Macau, the Chinese gambling enclave.

On Monday, Mr. Kim, 45, met his end at Kuala Lumpur International Airport in Malaysia. According to the National Intelligence Service of South Korea, he was poisoned by two women who appeared to be carrying out an assassination order from Pyongyang, the North Korean capital. Mr. Kim died on his way to the hospital. Two women have been detained in connection with the killing.