When a poblano chilli is dried, it is called an ancho chilli, both ancho and mulato are poblano dried poblano chilies. The difference between the two is that ancho gets picked when they ripen and then dried; the mulato on the other side is left on the plant to farther ripen till it becomes dark brown and then harvested. In terms of flavour profile that makes the ancho chili sweeter and fruiter than the mulato, which is also smokier.
This chilli actually has two distinct flavours – the outside skin has a sweet, raisin-like taste, and the inner part is moderately spicy. It can be used to add low to moderate heat to your dish, with a Scoville heat rating (SHU) of 1500-2500 it is not overly spicy. Actually, it is much less spicy than your typical jalapeño and it is a tad less spicy than mulato chili.
Ancho chillies are part of the Holy Trinity of Mexican chillies used to make delicious mole. The other two are Mulato and >Pasilla chilies.