Uddhava names Drona, Bhishma, Arjuna and Bhima as the roots of the Kurukshetra force, which is why he says the earth's burden is not yet removed: 'yad droNa-bhIShmArjuna-bhIma-mUlaiH' (SB 3.3.14).
King
Bhima
भीम
Bhima is the Pandava counted among the four roots of the Kurukshetra force. At SB 3.3.14 Uddhava says the earth's burden is not yet removed, because with Drona, Bhishma, Arjuna and Bhima as its roots the intolerable force of the Yadus, eighteen akshauhinis strong, still remains: 'yad droNa-bhIShmArjuna-bhIma-mUlaiH / aShTAdashAkShauhiNiko madAmshaiH rAste balaM durviShahaM yadUnAm'.
Śrīmad Bhāgavata Mahāpurāṇa 3.3.14 — Sanskrit Wikisource (pinned chapter page; Devanagari from the cross-validated transcription in validation/sanskrit_skandha3.json)
One of the four roots of the akshauhini force