Whose footprints is the speaker referring to in the poem?

In the seventh and eighth verses of this poem, the speaker mentions “footprints on the sands of time,”

…that perhaps another,Sailing o’er life’s solemn main,A forlorn and shipwrecked brother,Seeing, shall take heart again.

These footprints are the legacies we leave behind when we die—the things that we have achieved in life, lessons we have learned and records we have filled. By mentioning these footprints the speaker is rallying the audience to become...

In the seventh and eighth verses of this poem, the speaker mentions “footprints on the sands of time,”

…that perhaps another,
Sailing o’er life’s solemn main,
A forlorn and shipwrecked brother,
Seeing, shall take heart again.

These footprints are the legacies we leave behind when we die—the things that we have achieved in life, lessons we have learned and records we have filled. By mentioning these footprints the speaker is rallying the audience to become like “great men” of the past, those whose memories serve as inspirations to the living. These men also have left footprints—indications that we can make our own lives great, just as they did. And in becoming great ourselves, we also will become inspirations to some “forlorn and shipwrecked brother," a dejected member of a newer generation, who will follow the footprints we made, and will himself achieve success.

So, these footprints are metaphorical—they are the memories of great deeds and good men that get cemented in history, to serve as an inspiration for us all to seize life and experience it to its greatest extent, rather than let it pass us by. And, the speaker stresses, by allowing ourselves to be inspired by these past events, we ourselves are becoming inspirations for others.