A number of beliefs arose concerning the lives of various of the greatest Bodhisattvas and their current whereabouts and degree of contactibility. They were venerated and indeed contacted (allegedly). The realm of earth into which Siddhartha came is called Saha for these purposes. By its nature it only permitted Siddhartha to teach for about 50 years as he was a man on earth.
As I mentioned in a recent post, however, Mahayana Buddhists learn there are other better purer realms in which Buddhas and Bodhisattvas now live and sometimes they rule that entire realm and are able to teach for hundreds of years. Amitabha is the best known and apparently the greatest (as I mentioned in an earlier post). His name in Japanese is Amida (for those who were wondering - since in an earlier post I mentioned the alleged supernatural power of repeating his name in Japanese). He rules the Western pure Buddha-realm also called the ‘full of bliss’ realm (Sukhavati). The Pure Land scriptures that I’ve mentioned contain the most details of all of this.
The order of the development of cults is interesting. The first object of worship was the coming Buddha, Maitreya, but his cult has been overtaken by others. Next came the great Amitabha. His cult is still going strong. Avalokitesvara is a Buddha (or a Bodhisattva, depending on who you ask) and the 14th Dalai Lama is believed by his followers to be a re-birth of Avalokitesvara (as are the 1st to the 13th). Avalokitesvara seems to be believed to have manifested himself in many forms (and again, depending on whom you ask, he may himself be a manifestation of Amitabha or Amitabha may be a manifestation of him).
There are thought to be five ‘families’ of Buddhas and Siddhartha is regarded as being of the "Lotus" family.
Also icons of various Bodhisattvas came to be standardised so you could tell (if you knew the iconography) who was being depicted and why. For example the fat Buddha we know isn’t Siddhartha (i.e. the historical Buddha). He hasn’t yet become a Buddha and will be known as Maitreya in about 8,000 years once he is born on earth. In earlier posts I’ve given images of the Buddas Manjusri and Amitabha. Manjusri is usually depicted with the sword as in the image I provided. Avalokitesvara is often depicted with many heads and many arms with eyes on them. In some cases, one of the heads is thought to be the head of Amitabha. Here is one e.g:
Avalokitesvara with many heads and arms (from Vietnam and Wikipedia)
Tara is a female Buddha (or, again, possibly a Bodhisattva). She, too, is said to have manifested herself many times incarnately as indeed we all have (around 21 or 22 known times at least in Tara's case). You will usually see her depicted with green skin as in the following image from Wikipedia. She is also usually depicted (as here) moving her foot down so she can get up from her lotus position and help people. She’s another Tibetan favourite:
If you see a red Buddha it’s likely to be Amida (the Japanese version of Amitabha) (see below) but the Tibetans also have a love affair with him as one can imagine given his relationship with Avalokitesvara: