Pollito is Eduardo Perez's pet chicken, and also the mascot of his "Salsa y Salsa" Mexican restaurant.  He* also happens to be a guard chicken, serving after hours in the same capacity as a guard dog might (and nearly as effectively, it turns out!).  He learns very quickly to hate Gru, after he and Lucy Wilde sneak into the restaurant after hours looking for the PX-41 serum.  Every chance Pollito gets after that, he tries to attack Gru (and even Lucy).  This is one mean chicken!

Eduardo, however, describes him (much as any pet owner would their own pet) as "usually very friendly".  He's owned Pollito since he was a chick, and even included him in a picture with he and his mother, which hangs in the restaurant (as seen below).

* Pollito is described by Eduardo as "he", even though the character clearly is a hen.  For the sake of continuity, we've kept the gender as male in spite of appearances to the contrary.