You can put this question to Google and it will give you many answers. A lot of them are biographical answers. They tell you that he was an Austrian-born German philosopher and author of works in medicine, education, agriculture, as well as other branches of science. They describe his upbringing, his education and other significant events in his life.
But often when someone asks this question they are really asking why we, who draw on his work, see him as important. And to this question there are also many answers; perhaps everyone who values his work might have a different answer. Here’s one:
Rudolf Steiner called his studies spiritual science. He intended that we establish a science of the spirit every bit as exact as the science of the material world. But how do we do that? Someone once asked him “Why don’t I have more spiritual experiences?” to which he replied, “You have many, many spiritual experiences; you are just not aware of them”. This answer seems to correspond with the modern neurological view that we are only aware of a tiny bit of what our senses give us. Much of what we take in we are unaware of and process without being conscious of it.
In agriculture and horticulture we know of people who have developed their understanding to a very high degree and seem to us to have great intuition as to what to do in any circumstance. These are people who can see at a glance that a horse is lame, or that a cow is about to become sick, or that a plant needs a little water or that now is the right time to mow the orchard to get the best crop of fruit. Our language recognises such people in phrases such as “she has green fingers” or “he knows when livestock are ‘doing’”. These are people who have allowed the information that they are receiving to resonate within them until it is transformed into some kind of greater knowledge.
We also know of people who go the other way, and don’t do anything on the land unless they have a book that says so, or instructions on a packet or a can of spray. They reduce their farming or gardening to just a few variables so that they can cope with them; and this is what agricultural science does to some extent also (for good reason, in that case). A farm or garden can seem very simple and can sometimes be very simply described, using terms such as a “row of cabbages” or a “paddock of sheep”. But actually farms and gardens are incredibly complex systems of plants, animals (more livestock underground than above) nutrients and other characteristics. A fully representative computer model of a farm or garden might be as complex as planetary climate modelling, and is simply not possible on any practical terms.
So, while the learnings from agricultural science are extremely valuable, they are limited. We need something more, something we could call “nourished intuition.” And it is here that many of us see the value of Rudolf Steiner’s work. Because, though parts of it can be very difficult, it helps us train and feed our intuition. It helps us to be aware of some of the things we would otherwise miss; it helps us to think about them in radically different ways and it opens for us a path of development. And, what is particularly exciting about this process is that it leads to very practical results; practical in terms of yield, sustainability, plant and animal health for example.
So another answer to the question: “Who is Rudolf Steiner?” might be “He is someone whose work continues to inspire.”