Marcel Gilliard as the first Jaw Titan shifter was killed by a Titan when he arrived at Paradis Island. Well, the Titan who ate Marcel was Ymir who was a member of the Survey Corps troops with Eren and his friends.
Ymir was originally an Eldian who was banished to Paradis Island and injected with a Titan serum. This led Ymir to wander as a Pure Titan for 60 years on Paradis Island. However, after eating Marcel, Ymir was finally able to transform into a human again while gaining the ability to transform into a Jaw Titan.
This also makes Ymir decide to live a normal life like a normal human on Paradis Island and not use his Jaw Titan powers at all. Of course, this is in stark contrast to Marcel who plans to use the power of this little Titan to massacre the people of Paradis Island.
However, in the end Ymir was forced to transform into the Jaw Titan to save his comrades, including Historia. After his identity is revealed, Reiner and Bertolt kidnap Ymir to return the power of the Jaw Titan to Marley’s side. Ymir finally volunteered to go to Marley to restore the power of the Jaw Titan while protecting Reiner and Bertolt.