Did the Buddha actually teach much about compassion?

TheEccentric

Meaning the Gautama Buddha himself.

Or did the teachings about compassion come in later after his death from Mahayana teachers?

karasti

Compassion/Karuna is one of the 4 immeasurables which are contained in the Pali Canon.

http://www.accesstoinsight.org/tipitaka/kn/snp/snp.1.08.amar.html
http://www.accesstoinsight.org/lib/authors/nyanaponika/wheel006.html
http://www.accesstoinsight.org/tipitaka/kn/snp/snp.1.08.piya.html

Dakini

OP, perhaps what you have in mind is related to the Mahayana development of dedicating oneself to the liberation of all sentient beings. The original canon certainly includes teachings about compassion, but it doesn't take that final step of committing to the cessation of suffering for all beings.

However, studies of ancient Buddhist scrolls from Gandhara, a region in Pakistan and part of Afghanistan, reveal that the seeds of what later came to be called "Mahayana" were already sewn in the Buddha's time. Scholars say that what occurred is that different members of the sangha, or different factions, perhaps, were interested in different aspects of the Buddha's teachings, and emphasized those aspects in their studies, which ultimately came to be recorded in the Gandhari language. So we see the beginnings of a branching that ultimately lead to the development of two different schools: Mahayana and Hinayana (as it was called at the time). But according to scholars of the Gandhari scrolls, these co-existed as tendencies within the Buddha's community during his lifetime.

It's pretty fascinating. Here's a link to an earlier thread on New Buddhist about it:
http://newbuddhist.com/discussion/11592/significance-of-gandhari-scrolls-to-mahayana-theravada-split
Article on the research, from Tricycle magazine:
https://tricycle.org/magazine/whose-buddhism-truest/

lobster

One of the earliest authentic texts I favour is designed for rhino.
This advocates compassion for the individual practitioner initially ...

Here is the dharma history - many lost/assimulated bits ...
https://en.m.wikipedia.org/wiki/Early_Buddhist_schools

So to answer your question do Buddhas, that is the awake, advocate and practice compassion. The answer is universal and confirmed by the awake (the meaning of Buddha) in other traditions outside of the Buddhist class.

"Compassion? Yes!"