King Dasharatha of Ayodhya had three wives: Kausalya, Kaikeyi and Sumitra.
He performed a sacrifice to beget sons and as  a result, his queens became pregnant.
Lakshmana and his brother Shatrughna were born to Sumitra; while Rama and Bharata were born to Kausalya and Kaikeyi.

In the Puranas, Lakshmana is described as an incarnation of Shesha, the multiple-headed nāga (serpent) upon whom rests the god Vishnu, whose avatar Rama is considered.

When sage Vishwamitra takes Rama for killing the demons in the forest, Lakshmana accompanies them and goes to Mithila with them.
Lakshmana is specially attached to Rama.
When Rama marries Sita, Lakshmana marries Sita's younger sister Urmila.
They had two sons—Angada and Chandraketu.

Later, when Rama is exiled for fourteen years on the insistence of Kaikeyi, Lakshmana leaves his wife Urmila and joins Rama and Sita in exile.
King Dasharatha of Ayodhya had three wives: Kausalya, Kaikeyi and Sumitra. He performed a sacrifice to beget sons and as  a result, his queens became pregnant. Lakshmana and his brother Shatrughna were born to Sumitra; while Rama and Bharata were born to Kausalya and Kaikeyi.
In the Puranas, Lakshmana is described as an incarnation of Shesha, the multiple-headed nāga (serpent) upon whom rests the god Vishnu, whose avatar Rama is considered. 
When sage Vishwamitra takes Rama for killing the demons in the forest, Lakshmana accompanies them and goes to Mithila with them. Lakshmana is specially attached to Rama. When Rama marries Sita, Lakshmana marries Sita's younger sister Urmila. They had two sons—Angada and Chandraketu. 
Later, when Rama is exiled for fourteen years on the insistence of Kaikeyi, Lakshmana leaves his wife Urmila and joins Rama and Sita in exile.
Lakshmana