Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
後白河上皇と二条天皇の間をうまく渡り歩き、さらに摂政近衛基実と姻戚関係を結ぶなど、政界に於ける地位を上昇させていったのはだれか

### Response:

平清盛