Who in the Bible had multiple wives at the same time? Did any prophets have multiple wives? Do any Jewish or Christian sects still allow multiple wives?
Jacob/Israel did, and so did David and Solomon. Abraham only had one wife, but he had concubines. There are probably some other people in the bible who did too, but I can’t think of any right now. Oh, also Herod the Great, who shows up briefly in the New Testament had 10 wives, according to Josephus, at the same time.
Polygamy is still practiced by some Yemenite Jews and (theoretically) some Sephardim. For practical purposes, it was outlawed among Ashkenazi Jews by Rabbi Gershom around the year 1000. (Interestingly enough, Rabbi Gershom’s wrote his ban to expire in 1260, but it’s still followed.) As for Christians, it’s still practiced by some groups that split off the main LDS/Mormon church, but the main LDS/Mormon groups, including the LDS, and the RLDS, don’t allow it.
Abraham took Hajar/Hagar as a wife after Sarah could not have a child (or so they thought).
The only nominally christian sect that is polygamist I am aware of is the FLDS, a breakaway sect of the mainstream Mormon church who live in an isolated area on the Arizona/Utah border.