Shatrughna was son of Dashrath and Sumitra and he was twin brother of Laxmana. Just like how Laxmana supported Shri Ram, Shatrughna supported Bharat. While Bharat was staying in Nandigram, Shatrughna was protecting Ayodhya on his behalf but the original ruler being Shri Ram as Bharat had declared he was only the regent of the throne till Shri Ram was in the exile.
Later, in Uttar Kand, Shatrughna was sent to Madhura to defeat Lavanasura (son of demon Madhu and Kumbhinasi). Kumbhinasi was cousin of Ravana and she was abducted by Madhu and eventually got married to him and Ravana initially was angry (hypocrisy at its peak) but got pacified when Kumbhinasi begged him to forgive her husband.
Shatrughna attacked Lavanasura and defeated him and captured Madhura and he established the region of Shurasena and Madhura eventually turned into Mathura.
Shatrughna was the first person to know the real identity of Lava and Kusha as he halted at Valmiki Ashram and met Mata Sita and took her blessings. He was happy to see the children of his eldest brother.
Shatrughna and his wife Shrutkirti had two sons, Subahu and Shatrughati. Subahu ruled the region of Madhura while Shatrughati was sent to Vidisha. Shatrughati is known as Yupaketu in Ananda Ramayana and he married Naga Princess Malti and Princesses Madansundari, Princess of Shivkantipuri and daughter of King Kambhukanth. Subahu was married to Naga Princess Kamala and Gandharva Princess Achala.