Bertrand Russell, of all people, formulated what constitutes the kicking-off point of Ultimate Event Theory :

“From all this [‘all this’ being a discussion of Relativity] it seems to follow that events, not particles, must be the ‘stuff’ of physics. What has   been thought of as a particle will have to be thought of as a series of events.
(…) Thus ‘matter’ is not part of the ultimate material of the world, but merely a convenient way of collecting events into bundles.”
Bertrand Russell,  A History of Western Philosophy p. 786 Unwin Paperback Edition)

But Russell  does not follow up this particular line of thought. As for Einstein, his basic philosophic position is not easy to distinguish but seems to have been that ‘fields’ were the primary reality. Ultimately everything was part of a single ‘Unified Field’ which was continuous, and ‘matter’ was merely “that portion of the field wheich is particularly intense”. This conflicts with the basic intuition of Ultimate Event Theory that reality is discontinuous, made up of discrete bundles of ultimate events. However, these may be viewed as disturbances of an underlying, invisible, all-pervading substratum which is continuous, somewhat in the manner that ripples or foam are discrete disturbances of a fluid that is continuous, or at any rate appears so to us.

Whitrow, in one of his numerous books on time, advances the idea of a minimal unit of time, the chronon, and suggests a plausible value based on the diameter of an elementary particle divided by c the speed of light — this was the first time I came across the idea. He also has some useful comments to make on the illogicality of calculus always treating time as a continuous variable but, once again, he baulks at departing so far from tradition as to introduce the idea of radical discontinuity into physics.
More recently, in his very remarkable book, A New Kind of Science, Stephen Wolfram writes:
The only thing that ultimately makes sense is to measure space and time taking each connection in the casual network to correspond to an identical elementary distance in space and elementary distance in time.
One may guess that this elementary distance is around 10 (exp -35) meters , and that the elementary time interval is around 10 (exp -43) seconds.”    (p. 520)
He draws the conclusion :
“Whatever these values are, a crucial point is that their ratio must be a fixed speed, and we can identify this with the speed of light. So this means that in a sense every connection in a causal network can be viewed as representing the propagation of an effect at the speed of light.”
This certainly is a crucial point but I would prefer to see this fixed ratio as defining the operation of causality as such : it is a speed barrier which no effect propagated from one ultimate event to another can exceed, or even attain. (It is not necessary to identify the actual speed of light with this ‘maximum transmission speed’ for all physical or informatioonal processes : light, likewise other particles such as neutrinos, approach but do not actually reach this speed, which allows us to attribute them a small mass.)
It is not clear, to me anyway, whether Wolfram sees his ‘causal networks’ as being fundamental or the nodes that compose them and he does not actually stipulate that they should be events rather than objects.

More recently still, Lee Smolin writes

“If space and time consist of events, and the events are discrete entities that   can be counted, then space and time themselves are not continuous. If this is true, one cannot divide time indefinitely. Eventually we shall come to the elementary events, ones which cannot be further divided and are thus the simplest possible things that can happen. Just as matter is composed of atoms,  which can be counted, the history of the universe is constructed from a huge  number of elementary events.”
(Lee Smolin, Three Roads to Quantum  Gravity p. 41-2  Phoenix Paperback Edition)

However, Lee Smolin  writes in another place:

“A causal universe is not a series of stills following on, one after the other. [Why not?] There is time, but there is not really any notion of a
moment of time. There are only process (sic.) that follow one another by causal necessity.”  (Ib. p. 55)

Lee Smolin thus, seemingly, pins his faith on ‘processes’ rather than ‘ultimate events’, whereas, for me, a process is simply a tightly connected chain of  events  : it is the constituent ultimate events that are fundamental, not  the ensemble.

Also, Lee Smolin, reverting to a conception of Leibnitz, dispenses with the independent existence of what I call the Locality :

“There is no meaning to space that is independent of the relationships among  real things in the world. Space is not a stage [Why not?], which might  be empty or full, onto which things come and go. Space is nothing apart from the things that exist; it is only an aspect of the relationships that hold  between things.” Ib.  p. 18

I don’t see this. If anything at all happens, it must happen somewhere and this ‘somewhere’ must seemingly already on some sense exist, otherwise nothing could happen at all ! Smolin even goes so far as to attack the very idea of Space-Time having a ‘structure’ — an idea one finds on almost every page of textbooks on Relativity — as ludicrous and declares, quite incorrectly, that this never was Einstein’s conception. From my point of view, reducing Space-Time to ‘relations’ is throwing out the baby, not the bathwater. What Smolin views as the fiction, ’empty space’, is the primary reality while ‘relationships among real things in the world’ are not even a secondary reality : they are still farther down the actuality scale, coming after the ‘real things’ themselves, whatever they are.   S.H.