He is almost a 'midnight's child' (those born on the eve of Independence, Aug 14, 1947). He was born on Aug 12, 1948, a couple of days before India was one year old. Wikipedia summarises him rather well. The following paragraphs are from the Wiki entry for the new Karnataka Chief Minister.

K. Siddaramaiah was born in a remote village called Siddaramanahundi in Varuna Hobli of Mysore District. He's a leader of the Kuruba community, the third largest in Karnataka.

Siddaramaiah was a practising advocate in Mysore, and also taught law for some time. In 1978, Siddaramaiah began his political career when he was elected to the Mysore Taluk Board. Contesting on a Bharatiya Lok Dal ticket from Chamundeshwari constituency, he entered the 7th Karnataka Legislative Assembly in 1983. His was a surprise victory and it earned him name and fame in the Old Mysore region.

Later he joined the ruling Janata Party and became the first president of Kannada Watchdog Committee (Kannada Kavalu Samiti) set up to supervise the implementation of Kannadaas official language. During the mid-term polls in 1985, Siddaramaiah was re-elected from the same constituency and became Minister for Animal Husbandry and Veterinary Services. In Chief Minister Ramakrishna Hegde's government, he handled diverse portfolios such as Sericulture, Animal Husbandry and Transport portfolios
during different stages.

He first suffered defeat in 1989 Assembly elections when Congress' Rajashekaramurthy won. Later in 1992, he was appointed as Secretary General of Janata Dal, which gained strength after H. D. Deve Gowda joined hands with Hegde.

He was elected again in the 1994 State Elections and became the Minister for Finance in the Janata Dal government headed by Deve Gowda. He was made Deputy Chief minister when J. H. Patel became Chief Minister in 1996. After the split in the Janata Dal, he joined the Janata Dal (Secular) faction of Deve Gowda and became the president of its state unit. However, he lost in the 1999 state elections. In 2004, when the Indian National Congress and JDS formed a coalition government with Dharam Singh as Chief Minister, he was again appointed as Deputy Chief Minister.

In 2006, after differences with his mentor Deve Gowda, Siddaramaiah joined the Congress. He won the Chamundeshwari bypolls by a margin of 257 votes.
In the 2008 state Assembly elections, he contested from Varuna Constituency and was re-elected for the fifth time. He won 2013 election from same constituency on 8th May 2013. As reports suggested, he was a strong contender for the position of CM of Karnataka and was elected as the Chief Minister on 10th May 2013. He was elected as the leader of the Congress legislative party in the Karnataka assembly on 10 May 2013.

He announced that 2013 assembly election would be his last election.
He is married to Parvathi and has two sons. His younger son Yathindra is a doctor. He is an atheist.