I'm going to be boring, and quote Wikipedia:

At the beginning of episode two onwards, Mr. Bean falls from the sky in a beam of light, accompanied by a choir singing Ecce homo qui est faba ("Behold the man who is a bean "). These opening sequences were initially in black and white in episodes 2 and 3, and were intended by the producers to show his status as an "ordinary man cast into the spotlight". However, later episodes showed Mr. Bean dropping from the night sky in a deserted London street, against the backdrop of St. Paul's Cathedral suggesting Bean is an alien. Atkinson himself has acknowledged that Bean "has a slightly alien aspect to him"; in the animated series, he was actually shown to be an alien.