Kuber, the Lord of Wealth, was the stepbrother of Ravana and the actual ruler of Lanka. Ravana fought Kuber to then conquer Lanka!

Lord Brahma produced ten Prajapatis, or mind-born sons when he created the Universe. These ten were the father of the human race and one of them was Sage Pulatsya, the father of Vishrava. Vishrava – a sagacious scholar, mesmerised Rishi Bhardwaj so much that he offered his daughter Ilavida to Vishrava for marriage. Ilavida gave Vishrava a son, Kuber, the Lord of Wealth.
An asura Sumali and Tataka, decided that their daughter Kaiseki should marry the most virtuous man and hence they planned a meeting of Kaiseki and Vishrava. He fell in love with her and fathered Ravan and his brothers. Hence, Ravan was a Brahmasura.
Vishwakarma, the architect of Universe, created Lanka for Shiva; and Vishrava later asked it from Shiva as a dakshina. Vishrava’s son Kuber then inherited Lanka and shared all his wealth his half-brothers including Ravan. However, after getting all kinds of booms from Brahma, Ravan considered himself the most powerful of the lot and demanded entire Lanka from Kuber. When Kuber did not pay heed to his demands, Ravan fought Kuber and conquered Lanka.
Later, after killing Ravan, and returning to Rameshwar, Lord Ram created the Shiva Temple so as to reimburse his sin of Brahmanhatya.