Strong negative connotation when applied to people — 死硬派 (sǐyìngpài) means a 'diehard faction' or 'hardliners', a stock phrase in political commentary. Compare with 顽固 (wángù, stubborn), which is similar but slightly milder.
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死 (dead/extreme) + 硬 (hard) — 'dead hard'. The 死 here is a common intensifier meaning 'to the death; utterly': 死板 (rigid), 死活 (stubbornly), 死心 (give up entirely).
