Wholesome, good-humoured, jokey, smart, and kind, Jonas has been James's assistant as well as the Lone Wanderer and James's friend for as long as the Lone Wanderer, who got along with Jonas famously, can remember.
In the late 2260s, Jonas was appointed to be James' assistant by the Overseer, who hoped he would be a voice of reason. Jonas and James forged a friendship very quickly and together they worked at examining and treating patients, as well as conducting routine experiments testing the health of the Vault. For an unknown length of time, James deliberately kept his assistant in the dark about covert experiments aimed at reviving Project Purity. Eventually, Jonas grew suspicious of the physician's activities and by mid-2274, Jonas was willingly aiding James with experiments related to Project Purity.
After James escapes from Vault 101, Jonas is killed by Officer Mack for helping James open the Vault and trying to escape with him.
Growing Up Fast: Jonas is first encountered during the Lone Wanderer's 10th birthday when James takes the Lone Wanderer down to the generator room to give him or her a present (a BB gun). Jonas later takes a picture of the two.
Escape!: The Note from Dad holodisk can be taken from Jonas's body, containing a message pertaining to James' escape.
After the Lone Wanderer receives a BB gun for their 10th birthday and kills the radroach, Jonas is able to be punched or shot until he is unconscious. However, he will still take the photo of the Lone Wanderer and their father while he is unconscious.