(1) The teachings of Buddha, 6th century B.C..
As pointed out by Rajib, while the Principal Teachings of Buddhism may not directly strive for greater equality, but during the time of its inception Buddhism rose as an opposing force to Vedic Brahmanism and certainly held "equality" as one of its primary objectives. So Gautam Buddha makes a case for the pioneers for espousing equality.
Some of the fundamentals of the teachings attributed to Gautama Buddha are:
The Four Noble Truths: that suffering is an ingrained part of existence; that the origin of suffering is craving for sensuality, acquisition of identity, and annihilation; that suffering can be ended; and that following the Noble Eightfold Path is the means to accomplish this;
The Noble Eightfold Path: right view, right intention, right speech, right action, right livelihood, right effort, right mindfulness, and right concentration;
Dependent origination: the mind creates suffering as a natural product of a complex process;
Rejection of the infallibility of accepted scripture: Teachings should not be accepted unless they are borne out by our experience and are praised by the wise.
Anicca (Sanskrit: anitya): That all things that come to be have an end;
Dukkha (Sanskrit: duḥkha): That nothing which comes to be is ultimately satisfying;
Anattā (Sanskrit: anātman): That nothing in the realm of experience can really be said to be "I" or "mine";
Nibbāna (Sanskrit: Nirvāna): It is possible for sentient beings to realize a dimension of awareness which is totally unconstructed and peaceful, and end all suffering due to the mind's interaction with the conditioned world.
(2) Besides, the edicts of Emperor Ashoka , a devout of Buddha from the 3rd Century B.C. also qualify.
He is said to have turned a pacifist and converted to Buddhism after witnessing the mass murders in the battle of Kalinga. The edicts describe in detail Ashoka's views on "dhamma", an earnest attempt to solve some of the problems that a complex society faced, besides the extent of proselytism campaigns he carried out.
Dharma is good, but what constitutes Dharma? (It includes) little evil, much good, kindness, generosity, truthfulness and purity. Pilar Edict Nb2 (S. Dharmika)
And noble deeds of Dharma and the practice of Dharma consist of having kindness, generosity, truthfulness, purity, gentleness and goodness increase among the people. Rock Pilar Nb7 (S. Dharmika)
The full translation of the edicts could be found here
(3) Confucius, 6th century B.C., was one of the pioneers of humanism, and his teachings, later structured into Confucianism became an integral part of Chinese thought.