Mukherjee was sidelined from the Congress during the premiership of Rajiv Gandhi , Indira Gandhi 's son . Mukherjee had viewed himself and not the inexperienced Rajiv , as the rightful successor to Indira following her assassination in 1984 . Mukherjee lost out in the ensuing power struggle . He formed his own party , the Rashtriya Samajwadi Congress , which merged with the Congress in 1989 after reaching a consensus with Rajiv Gandhi . After Rajiv Gandhi 's assassination in 1991 , Mukherjee 's political career revived when Prime Minister P. V. Narasimha Rao appointed him Planning Commission head in 1991 and foreign minister in 1995 . Following this , as elder statesman of the Congress , Mukherjee was the principal and architect of Sonia Gandhi 's ascension to the party 's presidency in 1998
assassination in 1991
Assassination of Rajiv Gandhi
Pranab Mukherjee