Gulliver's didn't reveal the name his country and posed as a Hollander at Luggnag. Why did he do so ? What light does this throw on his character ?

The king of Luggnag is capricious and acts to do whatever he wants to his subjects. Gulliver has learned to act however he has to to protect himself and accomplish his final goal which is to get back home. Swift is trying to show people at their worst and highlight all of their flaws. Gulliver having to lie shows us what people often have to do to survive in the world as they try to navigate the lives of the people they interact with.