Jaqen H’ghar appears at the beginning of the series as a criminal from Lorath who is being taken north to The Wall by Yoren. He and two other criminals are locked in a wooden cart. Arya Stark, disguised as ‘Arry is also in the party traveling north.
Jaqen H’ghar uses an unusual method of speech where he doesn’t use anyone’s name, for example, he refers to himself and Arya as ‘a man’ and ‘a girl.’
He assists and befriends Arya Stark
Jaqen H’ghar and Arya build up a relationship after she first gives him a drink of water and then rescues him and his fellow captives after a fire breaks out near their cart. After the death of Yoren, they were all taken to Harrenhal.
He tells Arya that she can name three people to be killed as repayment for the three lives she had saved. On Arya’s request, Jaqen H’ghar killed firstly the torturer named ‘the Tickler’ then Ser Armory Loch.
Jaqen H’ghar initially refused Arya’s request to help her escape but was surprised and horrified when his refusal led to her request that he kill himself as her third death. He then agreed to help Arya escape, killing the guards at Harrenhal then leaving Harrenhal himself.
He is part of a shadowy group
Jaqen H’ghar waited on a rock for Arya to pass. He offered to take her to Braavos to be trained as a Faceless Man. After Arya declined, he gave her a coin and told her that if she changed her mind to say the words ‘Valar Morghulis’ and she could get passage to Braavos. Jaqen then removed his face revealing himself to be a Faceless Man.
Jaqen H’ghar then changed appearance and returned to the House of Black and White in Braavos.
When Arya later arrived at the House of Black and White, Jaqen said that he was ‘no one.’ Arya was admitted to the House to begin her training. Jaqen set Arya many tasks including assassinating people he names. Jaqen smiled after Arya killed the waif and announced she was returning to Westeros.