Believing
"The Electric Monk was a labour-saving device, like a dishwasher or a video recorder. Dishwashers washed tedious dishes for you, thus saving you the bother of washing them yourself; video recorders watched tedious television for you, thus saving you the bother of looking at it yourself; Electric Monks believed things for you, thus saving you what was becoming an increasingly onerous task, that of believing all the things the world expected you to believe." - Douglas Adams, Dirk Gently's Holistic Detective Agency (1987)
Gullibot, or: you better believe it
In his lesser-known book series, Douglas Adams poses the idea of a robot that is programmed to believe to take this burden from regular people. This specific example is a religious figure, but believing things is not limited to the realm of faith and religion. It can be belief about metaphysics, mathematical axioms, politics, science, news, rumours and stories. We as humans believe things all the time to be able to navigate our environment and make space for ourselves. We believe that the ground before us is solid so we can walk; we believe that the political party we vote for aligns with the way we think a country should be run; we believe that all birds on earth have been replaced by surveillance drones under the Raegan administration resulting in the fact that bird watching goes both ways now, and so on.
Taking the least complex example for devising a creature, I would imagine a little bot on wheels that could move around on the ground without bumping in to stuff. As soon someone told it 'The floor is lava!' the bot would screech 'It burns!' and move around faster. It would continue to do so until it was told that the floor is solid again. Of course, as the floor in fact does not turn into lava and the bot can still move around with ease, this is a demonstration of believing something blindly as well as believing contradictory things at the same time. We can laugh at the silly bot, but that would make us humans a bit hypocritical.