So, real quick, the commedia dell’arte is a very early form of professional theatre, that involved specific stock character roles which are largely reflected by the Fatui harbingers via their titles/codenames. Notably, the story of these plays always revolves around two actors that are not reflected by the Harbingers, the Innamorati (lovers), whom the story follows. Our Harbingers are found within the other three classes of actors though. The Zanni, which are the lower class (the harbingers from this group are Pierro, Pulcinella, Scaramouche, Tartaglia, Arlecchino, and Columbina); the Vecchi, which are often wealth and/or older characters (Pantalone and Dottore); and the Il Capitano, who are self-styled captains and braggarts (Capitano himself, La Signora, and sometimes the Scaramouche character). 

Our Tartaglia, also known as Childe or by his actual name, Ajax, is Rank 11 within the Fatui Harbingers. Within the commedia dell’arte the Tartaglia character is typically placed in the same area as the characters who have a higher high social status (The Vecchi) along with Pantalone and Dottore, or as a variant of the Innamorato (male lover) of the story. His precise social status can range from low, middle, to high income with his occupation and role within the story, though he is frequently a salesman. The Tartaglia character is also often far-sighted and has a minor stutter. This stutter often results in him being quick to anger as he also often has a large number of lines arranged so that he is frequently giving long speeches that he stumbles through. One of his primary emotions, in his most basic role, is that of frustration. Interestingly, the Tartaglia character is often put in a group with the Scaramouche and Pulcinella characters as being notably Neapolitan in terms of his character’s mask style.

In regards to other levels of characterization, when placed in a more important role such as the Innamorato, the Tartaglia character is often socially awkward and may even have a lack of confidence. He is also sometimes a bumbling character and, in some cases, his bumbling serves to get in the way of the Innamorati in some way whether he is the Innamorato or a side character.

It is worth noting that, for the most part, the Tartaglia character appears to fill roles as he is needed. Sometimes replacing the Il Dottore, as a secondary older man to Pantalone’s Vecchi role, the male Innamorato to the female Innamorata, or simply as a bit of a gag character for added comedy to the story.

The Genshin Impact Tartaglia is probably the Harbinger that differs the most from his commedia dell’arte stock character, though this is not to say that he doesn’t share some similarities. Our Tartaglia doesn’t really have a stutter, which is arguably the most notable aspect of the stock character. He does, however, feign being a salesman and can be somewhat bumbling, as noted in the way he has created some messes for the Fatui (i.e. his behavior in the Liyue and even the Fontaine archon quests). Similarly, he has quite the temper when things do not go according to plan for him, as shown in the Liyue archon quest.

It is feasible that he is filling a more Innamorato (male lover) role, but this is rather doubtful due to the notable lack of any Innamorata (female lover) character to go with him. As such, it is difficult to make any predictions about our Tartaglia’s storyline or place within the Fatui or overarching plot of the game based on his corresponding stock character. Nonetheless, it is worth mentioning that he could be acting as somewhat of a gag/side character in the way he keeps showing up all over Teyvat and is arguably the reason most of the Harbingers know so much about Traveler since he seemingly won’t stop talking about them. Furthermore, it is worth mentioning that he is largely portrayed to be sympathetic, if mildly problematic, within the Genshin storyline in regard to the Traveler and thereby the audience’s perspective.