Robert Adam Ross Maclennan, Baron Maclennan of Rogart, (26 June 1936 – 18 January 2020), was a British Liberal Democrat politician, formerly a life peer. He was the last leader of the Social Democratic Party (SDP), serving during the negotiations that led to its merger with the Liberal Party in 1988. He then became joint interim leader of the new party, known as the Social and Liberal Democrats (SLD) before later becoming the Liberal Democrats. He served as a Member of Parliament (MP) from 1966 to 2001, when he was elevated to the House of Lords.
He is also known as Robert Maclennan, Bob Maclennan and Robert Adam Ross MacLennan, Baron MacLennan of Rogart.
On 18 January 2020, it was reported that Maclennan had died at the age of 83.